to this Report on Form 6-K. Our actual results may differ materially from those contained in or implied by any forward-looking statements. Overview Silence Therapeutics plc ("we", "us", "our", "the Company" or "Silence")

Condensed consolidated income statement (unaudited)

Condensed consolidated statement of comprehensive income (unaudited)

Condensed consolidated balance sheet (unaudited)

Condensed consolidated statement of changes in equity (unaudited)

Six Months ended June 30, 2020 (unaudited)

Six Months ended June 30, 2021 (unaudited)

Condensed consolidated statement of cash flows (unaudited)

Notes to the financial statements

Six months ended June 30, 2021

Silence Therapeutics plc and its subsidiaries (together the Group') are primarily involved in the discovery, delivery and development of RNA therapeutics. Silence Therapeutics plc, a public company limited by shares registered in England and Wales, with company number 02992058, is the Group's ultimate parent Company. The Company's registered office is 27 Eastcastle Street, London, W1W 8DH and the principal place of business is 72 Hammersmith Road, London, W14 8TH.

These condensed interim financial statements were approved for issue on August 12, 2021.

These condensed interim financial statements do not comprise statutory accounts within the meaning of section 434 of the Companies Act 2006. Statutory accounts for the year ended December 31, 2020 were approved by the board of directors on March 31, 2021 and delivered to the Registrar of Companies. The report of the auditors on those accounts was unqualified, did not contain an emphasis of matter paragraph and did not contain any statement under section 498 of the Companies Act 2006.

The financial statements have not been reviewed or audited.

Basis of Preparation and Accounting Policies

Silence Therapeutics Plc transitioned to UK-adopted international accounting standards in its consolidated financial statements on January 1, 2021. This change constitutes a change in accounting framework. However, there is no impact on recognition, measurement or disclosure in the period reported as a result of the change in framework.

This condensed consolidated interim financial report for the half-year reporting period ended June 30, 2021 has been prepared in accordance with International Accounting Standard 34, Interim Financial Reporting' (IAS 34) as issued by the International Accounting Standards Board (IASB).

The interim report does not include all of the notes of the type normally included in an annual financial report. Accordingly, this report is to be read in conjunction with the annual report for the year ended December 31, 2020, which was prepared in accordance with international accounting standards in conformity with the requirements of IFRS's as issued by the IASB.

The accounting policies adopted are consistent with those of the previous financial year and corresponding interim reporting period.

The preparation of interim financial statements requires management to make judgements, estimates and assumptions that affect the application of accounting policies and the reported amounts of assets and liabilities, income and expense. Actual results might differ from these estimates.

In preparing these condensed interim financial statements, the significant judgements made by management in applying the Group's accounting policies and the key sources of estimation uncertainty are disclosed in the Critical Accounting Policies, Judgments and Estimates' section on Page 20.

The financial statements have been prepared on a going concern basis that assumes that the Group will continue in operational existence for the foreseeable future.

The 2020 coronavirus (COVID-19) pandemic became increasingly prevalent in Europe, the UK and the US where the Group's principal operations are conducted. Significant restrictions have now been imposed by the governments of those countries where the Group has operations, as well as the countries of external parties with which we conduct our business. In compliance with these restrictions, the Group and its employees have adapted to new working arrangements to ensure business continuity as far as is reasonably practicable in the short to medium term. This has so far proven to be effective, with Management maintaining a strong line of communication with all employees during this period.

The main risk posed to the Group by the pandemic is the potential slowing of Research & Development activities including possible knock-on delays in clinical trial data and sustained fixed costs during periods of relative inactivity. Whilst this would result in a lengthening of the Group's cash runway in the medium term, in the longer term these factors could limit the Group's ability to meet its corporate objectives. This risk is mitigated by the receipt of $60m ( 47.9 million) of the upfront payments in respect of the AstraZeneca collaboration and the $45m (net of expenses approximately $42.0 million / 30.8 million) from the private placement, both of which significantly increase the Group's baseline cash runway.

Based on the current operating forecasts and plans and, considering the cash, cash equivalents and term deposit at June 30, 2021, the Directors are confident that the Group has sufficient funding for the foreseeable future and at least one year from the date of these condensed interim financial statements. For this reason, they continue to adopt the going concern basis in preparing the financial statements.

Revenue from collaboration agreements for the 6 months ended June 30, 2021 relates to the Research collaboration agreements the Group entered into with Mallinckrodt plc in July 2019, Takeda Pharmaceutical Company Limited in January 2020 and AstraZeneca plc in March 2020.

Revenue for the 6 months ended June 30, 2021 comprised 5,677k of Research collaboration income (6 months to June 30, 2020: 995k) and 168k of royalty income (6 months to June 30, 2020: 151k).

Under our collaboration agreement with Mallinckrodt, we received an upfront cash payment of 16.4 million ($20 million) in 2019 and are eligible to receive specified development, regulatory and commercial milestone payments. We received milestone payments of 2.9 million or $4 million during the 6 months ended June 30, 2021. In addition to these payments, Mallinckrodt has agreed to fund some of our research personnel and preclinical development costs. We recognize the upfront payment, milestone payments, payments for personnel costs and other research funding payments over time, in accordance with IFRS 15. During the 6 months ended June 30,2021, we recognized a total of 3.8 million in revenue under this agreement.

Under our collaboration agreement with AstraZeneca, we received an upfront cash payment of 17.1 million ($20m) in 2020 with a further amount of 30.8 million ($40 million) received in May 2021. We recognize the upfront payment and milestone payments over time, in accordance with IFRS 15. During the 6 months ended June 30, 2021, we

recognized a total of 1.3m in revenue under this agreement.

We entered into a Technology Evaluation Agreement with Takeda on January 7, 2020 to explore the potential of our platform to generate siRNA molecules against a novel, undisclosed target controlled by Takeda. Under our collaboration agreement, we received a milestone payment of 1.6 million ($2 million) during the year ended December 31, 2020. We recognize the milestone payments over time, in accordance with IFRS 15. Our activities under the Technology Evaluation Agreement were effectively complete as of June 30, 2021. We may negotiate to enter into an exclusive follow-on license and collaboration agreement covering the Takeda target at some point in the future.

4. Segment reporting

Operating segments are reported in a manner consistent with the internal reporting provided to the Board. The chief operating decision maker (CODM), who has been identified as the Chief Executive Officer responsible for allocating resources and assessing performance of the operating segments.

For the 6 months ended June 30, 2021 and 6 months ended June 30, 2020, the CODM determined that the Group had one business segment, the development of RNAi-based medicines. This is in line with reporting to senior management. The information used internally by the CODM is the same as that disclosed in the financial statements.

5. Loss per ordinary equity share (basic and diluted)

The calculation of the loss per share is based on the loss for the 6 months to June 30, 2021 after taxation of 20,048k (6 months ended June 30, 2020: loss of 11,029k) and on the weighted average ordinary shares in issue during the year of 88,121,772 (6 months ended June 30, 2020: 80,619,119).

The options outstanding at June 30, 2021 and June 30, 2020 are considered to be anti-dilutive as the Group is loss-making.

7. Derivative financial instruments

Derivative financial instruments relate to an open forward currency contract measured at fair value through the income statement. The fair value was calculated from data sourced from an independent financial market data provider using mid-market-end-of-day data as of Close of Business date as December 31, 2020. The derivative contract in place at December 31, 2020 was closed out on May 28, 2021.

The fair value of the derivative is calculated based on level 2 inputs under IFRS 13.

The fair value of financial instruments that are not traded in active market, in the case an over-the-counter derivative, is determined using valuation techniques which maximize the use of observable market data and rely as little as possible on entity specific estimates. As all significant inputs required to fair value an instrument are observable, this derivative financial instrument is included in level 2.

The specific valuation technique used to value this derivative is the present value of future cash flow based on the forward exchange rate relative to its value based on the year-end exchange rate.

The derivative fair value movement is disclosed in the Income Statement under "Other (losses)/gains - net". For the six month period to June 30, 2021 the gain on the derivative financial instrument ( 1.02 million), which was closed out in May 2021, matched the related loss ( 1.02 million) on the receivable, resulting in a net nil impact on the Income Statement.

8. Contract liabilities

Contract liabilities comprise entirely deferred revenue in respect of the Mallinckrodt, Takeda and AstraZeneca plc Research collaborations. The current contract liabilities represent the amount of estimated revenue to be reported in

the next 12 months related to amounts invoiced to our partners. The current and non-current contract liabilities include only recharge expenses and milestones achieved through June 30, 2021.

A 2.3 million current tax asset was recognised in respect of research and development tax credits in the six months ended June 30, 2021 (six months ended June 30, 2020: 2.3 million). Additionally, the current tax asset expected to be received in respect of research and development tax credits for the year ended December 31, 2020 is 3.5 million.

10. Capital reserves

The Group has only one class of share. All ordinary shares have equal voting rights and rank pari passu for the distribution of dividends.

On February 5, 2021 the Group announced a Private Placement of 2,022,218 of the Company's American Depositary Shares ("ADSs"), each representing three ordinary shares of 5 pence each in the capital of the Company ("Ordinary Shares"), at a price of US $22.50 per ADS, with new and existing institutional and accredited investors (the "Private Placement"). The aggregate gross proceeds of the Private Placement was US $45 million (approximately 33 million) before deducting approximately 2.3 million in placement agent fees and other expenses. The financing syndicate included Adage Capital Management LP, BVF Partners L.P., Consonance Capital, Great Point Partners, LLC, and other investors.

The Group intends to use the net proceeds from the Private Placement primarily to support development of the Group's pipeline based on its messenger RNAi GOLD (GalNAc Oligonucleotide Discovery) Platform, and for general corporate purposes.

Details of the shares issued by the Company during the six months ended 30 June 2020 are as follows:

11. Related party transactions

Transactions between the Group and its subsidiaries, which are related parties, have been eliminated on consolidation and are not disclosed in this note.

During the six months to June 30, 2021 the Group paid nil (six months to June 30, 2020: 75k) to Gladstone Partners Limited, a company controlled by Director Iain Ross. The amounts payable were settled before the relevant period ends.

MANAGEMENT'S DISCUSSION AND ANALYSIS

You should read the following discussion and analysis of financial condition and operating results together with our unaudited financial statements as of and for the six months ended June 30, 2021 and the related notes to those financial statements included as Exhibit 99.1 to this Report on Form 6-K.

The statements in this discussion with respect to our plans and strategy for our business, including expectations regarding our future liquidity and capital resources and other non-historical statements, are forward-looking statements. These forward-looking statements are subject to numerous risks and uncertainties, including the risks and uncertainties described in Exhibit 99.1 to this Report on Form 6-K. Our actual results may differ materially from those contained in or implied by any forward-looking statements.

Silence Therapeutics plc ("we", "us", "our", "the Company" or "Silence") is a biotechnology company focused on discovering and developing novel molecules incorporating short interfering ribonucleic acid, or siRNA, to inhibit the expression of specific target genes thought to play a role in the pathology of diseases with significant unmet medical need. Our siRNA molecules are designed to harness the body's natural mechanism of RNA interference, or RNAi, by specifically binding to and degrading messenger RNA, or mRNA, molecules that encode specific targeted disease-associated proteins in a cell. By degrading the message that encodes the disease-associated protein, the production of that protein is reduced, and its level of activity is lowered. In the field of RNAi therapeutics, this reduction of disease-associated protein production and activity is referred to as "gene silencing." Our proprietary mRNAi GOLD (GalNAc Oligonucleotide Discovery) platform is a platform of precision engineered medicines designed to accurately target and silence' specific disease-associated genes in the liver, which represents a substantial opportunity. Using our mRNAi GOLD platform, we have generated siRNA product candidates both for our internal development pipeline as well as for out-licensed programs with third-party collaborators. In May 2021, we presented the first clinical data from our mRNAi GOLD platform that successfully translated the results from pre-clinical models into humans.

Our proprietary clinical programs include SLN360 designed to address the high and prevalent unmet need in reducing cardiovascular risk in people born with high levels of lipoprotein(a), or Lp(a), and SLN124 designed to address rare iron loading anemia conditions, thalassemia and myelodysplastic syndrome, or MDS. We are evaluating SLN360 in the APOLLO phase 1 single-ascending dose study in healthy individuals with high levels of Lp(a) 60 mg/dL. In August 2021, we announced complete enrolment in four cohorts of the SLN360 single-ascending dose study and we anticipate topline data in the first quarter of 2022. The APOLLO study protocol includes the option to add a fifth cohort if we want to learn more about the clinical profile of SLN360. We are evaluating SLN124 in the GEMINI II phase 1 single-ascending dose studies in patients with thalassemia and MDS. We anticipate topline data from both studies in the third quarter of 2022. In May 2021, we reported positive topline results from the SLN124 GEMINI healthy volunteer study, which was the first clinical data from our mRNAi GOLD platform. The SLN124 healthy volunteer study demonstrated safety and proof-of-mechanism to support the ongoing SLN124 phase 1 studies in patients with thalassemia and MDS.

Our partnered pipeline includes ongoing research and development collaborations with leading pharmaceutical companies, such as AstraZeneca PLC, or AstraZeneca, Mallinckrodt plc, or Mallinckrodt, and Takeda Pharmaceutical Company Limited, or Takeda. These collaborations collectively represent up to 14 pipeline programs and up to $6 billion in potential milestones plus royalties.

There are approximately 14,000 liver-expressed genes and only around one percent of them have been targeted by publicly known siRNAs. We aim to maximize the substantial opportunity of our mRNAi GOLD platform through a combination of building and advancing our proprietary and partnered pipelines. Through this hybrid model, we plan to significantly expand our portfolio of mRNAi GOLD platform programs by delivering 2-3 initial new drug applications per year from 2023.

Half-Year 2021 and Recent Corporate Highlights

Proprietary Pipeline

Upcoming Events and Anticipated Data Milestones

Collaboration Agreement with AstraZeneca

In March 2020, we entered into a collaboration agreement with AstraZeneca to discover, develop and commercialize siRNA therapeutics for the treatment of cardiovascular, renal, metabolic and respiratory diseases. Under this agreement, AstraZeneca made an upfront cash payment to us of $20.0 million in May 2020 (equivalent to 17.1 million as of the payment date) with a further 30.8 million ($40 million) received in May 2021. In March 2020, an affiliate of AstraZeneca also subscribed for 4,276,580 new ordinary shares for an aggregate subscription price of $20.0 million.

We anticipate initiating work on five targets within the first three years of the collaboration, with AstraZeneca having the option to extend the collaboration to an additional five targets. AstraZeneca has agreed to pay us $10.0 million upon the exercise of each option to collaborate on an additional target. For each target selected, we will be eligible to receive up to $140.0 million in potential milestone payments upon the achievement of milestones relating to the initiation of specified clinical trials, the acceptance of specified regulatory filings and the first commercial sale in specified jurisdictions. For each target selected, we will also be eligible to receive up to $250.0 million in potential commercial milestone payments, upon the achievement of specified annual net sales levels, as well as tiered royalties as a percentage of net sales ranging from the high single digits to the low double digits.

We continue to advance the research and development workplans for each identified target as scheduled and agreed to with our collaboration partner.

Collaboration Agreement with Mallinckrodt

In July 2019, we entered into a collaboration agreement with Mallinckrodt Pharma IP Trading DAC, a wholly owned subsidiary of Mallinckrodt plc, to develop and commercialize RNAi drug targets designed to silence the complement cascade in complement-mediated disorders. Under the agreement, we granted Mallinckrodt an exclusive worldwide license to our C3 targeting program, SLN500, with options to license two additional complement-mediated disease targets from us. Mallinckrodt exercised options to license two additional complement targets from us in July 2020.

While we are responsible for the Phase 1 clinical trial in each case, Mallinckrodt will be funding all of our research personnel costs on a full-time equivalent, or FTE, basis associated with preparing for and conducting the Phase 1 clinical trials. We are also responsible for the provision of drug product for preclinical activities and for the Phase 1 clinical trials, but any manufacturing expense relating to the Phase 1 trial will be paid for by Mallinckrodt. After completion of the Phase 1 clinical trials, Mallinckrodt will assume clinical development and responsibility for potential global commercialization.

The collaboration provides for potential additional development and regulatory milestone payments in aggregate of up to $100 million for the initial C3 target and up to $140 million for each of the two optioned complement-mediated disease targets, with such milestones relating to the initiation of specified clinical trials in specified jurisdictions, and upon the receipt of regulatory approvals by specified authorities, in each case for multiple indications. We are also eligible to receive potential commercial milestone payments of up to $562.5 million upon the achievement of specified levels of annual net sales of licensed products for each program. We are also eligible to receive tiered, low double-digit to high-teen percentage royalties on net sales for licensed products for each program. We received a research milestone payment of $2 million in October 2019 upon the initiation of work for the first complement C3 target. In September 2020, we received another $2 million research milestone payment following the initiation of work on a second complement target. In February 2021, we initiated work on the third complement target which triggered another $2 million research milestone payment. In April 2021, we received another $2.0 million research milestone for the initiation of the toxicology study for the first identified target.

In connection with the execution of this agreement, Mallinckrodt made an upfront cash payment in 2019 of $20.0 million (equivalent to 16.4 million as of the payment date). Under a separate subscription agreement, Cache Holdings Limited, a wholly owned subsidiary of Mallinckrodt plc, concurrently subscribed for 5,062,167 new ordinary shares for an aggregate subscription price of $5.0 million (equivalent to 4.0 million as of the payment date).

We continue to advance the research and development workplans for each identified target as scheduled and agreed to with our collaboration partner.

Financial Operations Overview

We do not have any approved products. Accordingly, we have not generated any revenue from product sales, and we do not expect to generate any revenue from the sale of any products unless and until we obtain regulatory approvals for, and commercialize any of, our product candidates. In the future, we will seek to generate revenue primarily from product sales and, potentially, regional or global strategic collaborations with third parties.

Under our collaboration agreement with AstraZeneca, we received an upfront cash payment of $20.0 million ( 17.1 million as of the payment date) and an additional payment of $40.0 million ( 30.8 million) in May 2021. We are also eligible to receive specified development and commercial milestone payments as well as tiered royalties on net sales, if any. We recognize the upfront payment and milestone payments over time, in accordance with IFRS 15. During the six months ended June 30, 2021, we recognized a total of 1.3 million in revenue under this agreement.

Under our collaboration agreement with Mallinckrodt, we received an upfront cash payment of $20.0 million ( 16.4 million as of the payment date) and are eligible to receive specified development, regulatory and commercial milestone payments. We received a milestone payment of $2.0 million ( 1.7 million as of the payment date) in 2020 and 2 other milestone payments totalling $4.0 million ( 2.9 million as of the payment date) in the first half of 2021. In addition to these potential payments, Mallinckrodt has agreed to fund some of our research personnel and preclinical development costs. We recognize the upfront payment, milestone payments, payments for personnel costs and other research funding payments over time, in accordance with IFRS 15. During the six months ended June 30, 2021, we recognized a total of 3.8 million in revenue under this agreement.

We entered into a Technology Evaluation Agreement with Takeda on January 7, 2020 to explore the potential of our platform to generate siRNA molecules against a novel, undisclosed target controlled by Takeda. Under our collaboration agreement, during the six months ended June 30, 2021 we received a milestone payment of nil (six months ended June 30, 2020: 0.4 million). We recognize the milestone payments over time, in accordance with IFRS 15. Our activities under the Technology Evaluation Agreement with Takeda were effectively complete as of June 30, 2021. We may negotiate to enter into an exclusive follow-on license and collaboration agreement covering the Takeda target at some point in the future.

In December 2018, we entered into a settlement and license agreement with Alnylam Pharmaceuticals Inc., or Alnylam, pursuant to which we settled outstanding patent litigation with Alnylam related to its RNAi product ONPATTRO. As part of the settlement, we license specified patents to Alnylam, and Alnylam pays us a tiered royalty of up to one percent of net sales of ONPATTRO in the EU. We are eligible to receive these royalties until 2023. We invoice Alnylam quarterly in arrears based on sales data for that quarter as reported to us by Alnylam. Royalty revenue is recognized based on the level of sales when the

related sales occur. During the six months ended June 30, 2021, we recognized a total of 0.2 million in royalty income from Alnylam.

Cost of sales consists of research and development expenditure that is directly related to work carried out on revenue generating contracts. This includes salary costs that are apportioned based on time spent by employees working on these contracts as well as costs of materials and costs incurred under agreements with contract research organizations, or CROs.

We classify our operating expenses into two categories: research and development expenses and administrative expenses. Personnel costs, including salaries, benefits, bonuses and share-based payment expense, comprise a significant component of each of these expense categories. We allocate expenses associated with personnel costs based on the function performed by the respective employees.

Research and Development Expenses

The largest component of our total operating expenses since inception has been costs related to our research and development activities, including the preclinical and clinical development of our product candidates. We expense research and development costs based on stage of completion and classify them as either direct or indirect.

Our direct research and development expense primarily consists of: