United Kingdom: Additional Information Form | Research Credit Integrity Alliance

This page explains the additional information form that must support a United Kingdom research and development (R&D) tax relief claim: its legal basis, when it is filed, who may file it, what it asks for, and the consequences of leaving it out. It describes the rules only and makes no recommendation.

Legal basis

Paragraph 83EA of Schedule 18 to the Finance Act 1998 gives HMRC power to specify by regulations the information required in support of an R&D claim. It was inserted by the Finance (No. 2) Act 2023 with effect for claims made on or after 1 August 2023.1 The Relief for Research and Development (Content of Claim Notifications, Additional Information Requirements and Miscellaneous Amendments) Regulations 2023 (SI 2023/813) provide, in regulation 3, that for claims made on or after 8 August 2023 the claimant must provide the information specified in Schedule 2. The information must be provided on or before the date the claim is made. No additional requirement applied to claims made between 1 and 7 August 2023.1

If the required information is not provided, the claim is invalid. HMRC's manual states that this applies to the merged R&D expenditure credit and enhanced R&D intensive support (ERIS), and also to claims under the older RDEC and SME schemes.1

HMRC lists the requirement to claim digitally and provide additional information among its policy changes, applying to claims from August 2023. It states that before the change around half of claimants did not provide any extra information alongside their claim, and that the changes help it to risk assess, process and pay claims more effectively.2

When and how it is filed

Rule	Detail
How	Through HMRC's online additional information form1
Timing	Before, or on the same day as, the Company Tax Return (CT600). If both are sent on the same day, the form must go first3
Frequency	At least once for each accounting period for which a claim is made. A period of account longer than 12 months needs a form for each accounting period within it13
Separate claims	A new form is needed for each claim when it is made, for example a claim to one scheme in the original return and a claim to the other in an amendment, or a claim that is withdrawn and made again1
Amended claims	No new form is required when a valid claim is amended, but HMRC says a new form supporting a material change, such as adding or removing a project, may reduce the risk of a compliance intervention1
Groups	Each company in a group needs its own Government Gateway account to submit a form; a Group Tax Manager account cannot be used3

After submission, HMRC sends an email confirming receipt with a reference number. The form cannot be accessed again once submitted.3

Who can file it

The form can be completed by a representative of the company or by an agent acting for it. An agent must first log in to its agent services account, and the company should give the agent permission to complete the form.3 HMRC's update history records that from 25 January 2024 an agent does not need to be authorized as the company's Corporation Tax agent through Online Agent Authorisation to provide the form.3

What the form asks

HMRC's manual sets out the questions by topic. In summary:1

Topic	Information required
Business details	Registered name, Corporation Tax Unique Taxpayer Reference, employer PAYE reference, VAT number, main type of business (SIC code), and further details for companies registered in Northern Ireland
Contact details	Name and role of the person completing the form, whether that person is the senior officer responsible for the claim, email and telephone; whether the company has a tax agent for the R&D claim and, if so, the agent's full name, business name, telephone number and email address
About the claim	Accounting period dates matching the return; whether it is part of a long period of account; the scheme claimed; qualifying expenditure by category; qualifying indirect expenditure; overseas externally provided workers and contracted out work; PAYE references for externally provided workers; details of companies to which R&D work was contracted out
ERIS claims	Eligibility; whether the company is exempt from the PAYE cap and why; qualifying expenditure by category; trading and operating expenses; capitalized R&D expenditure; connected companies and their expenditure
Projects	Number of projects; for each project described, its name, main field of science or technology, the existing knowledge it planned to improve, the advance sought, the uncertainties faced, how it sought to overcome them, and the qualifying expenditure

HMRC's public guidance describes the agent question more broadly. It asks for the contact details of all agents involved in the claim, including any agent who has given advice, analyzed costs, helped prepare technical assessments, or given information for or completed the online forms or the Company Tax Return.3 See Preparer identification.

Which projects must be described

Projects claimed	Projects to describe
1 to 3	All of them
4 to 10	At least 3, which together account for at least half of the qualifying expenditure claimed
More than 10	At least 3 accounting for at least half of the qualifying expenditure, but no more than the 10 with the highest qualifying expenditure if more would be needed

Source: HMRC guidance, "Project details to include".3 Where a company claims under two schemes, the required projects are described separately for each claim.3

For the project descriptions, HMRC explains that science excludes work in the arts, humanities and social sciences, including economics, and that from 1 April 2023 mathematical advances are treated as science. Uncertainties must be scientific or technological uncertainties for the industry, not just for the company.3

Quality of answers

HMRC's manual states that a response is not provided merely because a question has an answer in it. To meet the requirement, the response must address the question asked and give complete and relevant information.1 It is not acceptable to refer to documents or information held outside the form, for example "see R&D report", even if HMRC holds them, and nonsense responses are not acceptable.1 For the project questions, the manual states that a failure to answer satisfactorily will result in the claim being rejected as invalid.1

The form forms part of HMRC's risk assessment of each return. Incomplete or improper responses will be identified and increase the likelihood of an enquiry or other compliance activity.1 HMRC also uses the information to target high volume activity where it sees similar mistakes across many claimants.2 See Reviews and audits.

A company may also send a separate R&D report with further supporting detail, such as the claim methodology, any use of sampling and details of the competent professionals, by email or with the Company Tax Return.3

Consequences of a missing form

If the form is not submitted, the R&D claim will not be accepted. If the return is submitted before the form, the claim will be rejected, and HMRC will write to confirm that it will remove the R&D claim from the return. Close to the last date for amending the return, the company may not be able to make a valid claim for that accounting period.3 If the accounting period dates on the form and the return do not match where a mean accounting date election applies, the form will be rejected and the claim removed.3 See Disputes and appeals.

What the form does not ask

Neither the manual's list of questions nor HMRC's guidance asks how the agent is paid, how much it is paid, or whether its fee depends on the amount of the claim.13

Sources

HM Revenue and Customs, Corporate Intangibles Research and Development Manual, CIRD182000, "R&D Tax Reliefs: reformed reliefs: claims process: additional information form" (manual updated 25 August 2026), sections "Statutory framework", "When and how information is submitted", "What information is required" and "Failure to provide complete or proper responses". https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird182000 (accessed 11 October 2026). Back
HM Revenue and Customs, Approach to Research and Development tax reliefs 2023 to 2024 (published 30 October 2024), section 2.1 (Table 2) and section 2.4. https://www.gov.uk/government/publications/hmrcs-approach-to-research-and-development-tax-reliefs-2023-to-2024/approach-to-research-and-development-tax-reliefs-2023-to-2024 (accessed 11 October 2026). Back
HM Revenue and Customs, Additional information you must submit before you claim Research and Development tax relief (last updated 26 September 2025), update history and sections "Your accounting period", "When to submit", "Who can submit", "Company details to include", "Project details to include", "Describing each project", "Before you start" and "What you need to do next". https://www.gov.uk/guidance/submit-detailed-information-before-you-claim-research-and-development-rd-tax-relief (accessed 11 October 2026). Back