Cite this dataset: Parker, A. (2026). UK R&D Tax Relief Rule Timeline: Dated Record of Rule Changes Since the 2023-24 Reform. Zenodo. https://doi.org/10.5281/zenodo.22753341
Why this exists
An append-only record, not a rewritten summary
This timeline only adds entries once a change is confirmed against a primary source (gov.uk, legislation.gov.uk or an HMRC manual page), not from secondary commentary alone. Entries are never edited to remove a past event, only appended to or corrected in place with a visible correction note, so the record stays honest about what was known when.
The timeline
R&D-intensive SME enhancement begins (predecessor to ERIS)
A retrospective provision under the old SME scheme let R&D-intensive, loss-making SMEs claim a higher tax credit rate. This is a distinct, older arrangement from Enhanced R&D Intensive Support (ERIS), which only starts under that name a year later (see the 1 April 2024 entry). The intensity threshold here was 40% of total expenditure.
Additional Information Form becomes mandatory for every claim
Every R&D tax relief claim (SME scheme or RDEC) requires a digital Additional Information Form submitted before or on the same day as the Company Tax Return. Claims without one are removed from the return. Legal basis: the Relief for Research and Development (Content of Claim Notifications, Additional Information Requirements and Miscellaneous Amendments) Regulations 2023 (SI 2023/813).
Merged scheme and ERIS (by name) both begin
For accounting periods beginning on or after this date: the merged R&D expenditure credit scheme replaces the old SME/RDEC split for most companies; Enhanced R&D Intensive Support (ERIS) begins under its current legislative footing, with the R&D-intensity threshold easing from 40% to 30%; the subsidised-expenditure restriction that reduced relief for grant-funded R&D under the old SME scheme is removed entirely; and new restrictions on overseas contracted-out/externally-provided-worker costs begin, with a narrow, fact-specific exception.
HMRC publishes incorrect claim-notification guidance
HMRC's own published guidance on the claim notification requirement was wrong for this five-and-a-half-week window, causing genuine confusion about who needed to notify. This is the error window, distinct from the remedy window below.
Administrative easement window for affected notification periods
Companies whose claim notification period ended in this window, and who filed a valid R&D claim via an amended return (for a pre-April-2023 period) between 1 April and 30 November 2024, don't need to separately notify, despite technically being required to. This is the remedy for the guidance error above; contact HMRC's R&D Policy team directly to rely on it.
Adviser registration requirement begins phasing in
Advisers who interact with HMRC on a client's behalf, including R&D claim preparers, start falling under a formal registration requirement under the Finance Act 2026, Part 7 (Schedule 20 sets out the exemptions to it, not the requirement itself). Registration runs through each firm's HMRC Agent Services Account. There is no public lookup: HMRC's own registration guidance describes no mechanism for a client to check whether a firm is registered.
Targeted advance assurance pilot opens
HMRC introduces a targeted advance assurance service as a pilot, running until May 2027. SMEs can ask for assurance on up to 2 specific complex or high-risk areas of a claim (for example whether a project meets the R&D definition, overseas expenditure, or contracted-out work). Large companies can't apply. HMRC aims to process an application within 40 calendar days. Correction, 15 September 2026: this entry previously gave an unconfirmed end date of 31 May 2027; it now uses HMRC's own wording, "until May 2027".
Found something out of date? Rules change and we won't always catch it the same day. Tell us and we'll check it against the primary source and correct it here, with the correction visible, not quietly edited away.
Alternatives and limitations
This page tracks what changed and when. It doesn't tell you which rules apply to your specific claim, because that depends on your accounting period and circumstances. For that, see which scheme am I on, or schemes explained for the fuller picture.
