What accounting documents will be needed?

HMRC expects claims to be supported by detailed technical documentation, not just a summary of expenditure. A General Ledger Detail, often referred to as a nominal ledger, is a core part of that evidential base when claiming R&D for tax purposes.

This ledger should clearly identify qualifying expenditure and demonstrate how the expenditure links to specific R&D projects. It allows HMRC to see how costs align with eligible R&D activity and also how figures within the claim link back to the statutory accounts and Corporation Tax computation.

Where inconsistencies appear in the claim, HMRC may open an enquiry.

Good documentation does not create eligibility for R&D tax credits, it supports the claim. The absence of clear records can weaken a claim that could be valid.

HMRC expects the following supporting evidence to be available:

• Full CT600 and Corporation Tax computation – The submitted Corporation Tax return (CT600) and supporting computation showing how the R&D enhancement or payable credit has been calculated.
• Expense records – A detailed breakdown of qualifying expenditure categories. These include staff costs, consumables, software, externally provided workers and eligible subcontractors, with supporting invoices, contracts and payroll records.
• Timesheets or project tracking records – Evidence that demonstrates the proportion of staff time that was spent on qualifying activities, prepared or reviewed by a competent professional.
• Accounting records – Statutory accounts and management information. This  includes profit and loss statements, balance sheets and cash flow statements, in order to reconcile claim figures to reported financial results.
• Cost allocation methodology – A clear explanation of how expenditure has been apportioned between qualifying R&D and routine commercial activity, particularly where indirect staff or shared overheads are involved.
• Filed tax documentation – Copies of submitted returns and amended returns where the R&D relief is claimed.
• Additional Information Form (AIF) – Mandatory from August 2023, this must be submitted before or on the same day as the Corporation Tax return, providing project descriptions, qualifying expenditure totals and technical narratives.
• Claim Notification Form (CNF) – Required in certain circumstances, this must be filed within six months of the end of the accounting period to notify HMRC of an intention to claim relief.

The Claim Notification Form (CNF) is only required if the business is a first-time claimant, they have claimed before but the last claim was submitted more than three years after the end of the relevant period, or if the business is claiming for a period that started on or after 1st April 2023.

As 2026 progresses, HMRC’s use of digital verification checks is continuing to become more structured. Claims supported by contemporaneous records, clear allocation methodologies and consistent financial data are materially more defensible during the review process of an R&D claim.