R&D tax relief
The R&D rule timeline
Most published R&D content was written before, or never updated since, the 2023-24 reform. This page is an append-only, dated record of what actually changed and when. Each entry is sourced directly to gov.uk, legislation.gov.uk or an HMRC manual page, not to second-hand commentary.
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: section 223 of the Finance Act 2026 (Part 7) bars an unregistered adviser from interacting with HMRC unless an exception in Schedule 20 applies. Online registration rolls out in stages from 18 May 2026 to 31 March 2027. 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.
How to cite
Citing and reusing this dataset
The data is published under a Creative Commons Attribution 4.0 licence. You can quote it, republish it and build on it, commercially or not, as long as you credit it and link back. The DOI below points at the copy deposited on Zenodo on 14 September 2026. This page is the current version, and anything corrected since that deposit is listed in the methodology changelog.
- Reference list (APA style)
Parker, A. (2026). UK R&D Tax Relief Rule Timeline: Dated Record of Rule Changes Since the 2023-24 Reform [Data set]. Zenodo. https://doi.org/10.5281/zenodo.22753341
- In an article or report
Source: Established Finance, R&D Tax Relief Rule Timeline (establishedfinance.co.uk/rd-rule-timeline/), compiled by Adam Parker.
- BibTeX
@misc{parker2026rdtimeline, author = {Parker, Adam}, title = {{UK R\&D Tax Relief Rule Timeline: Dated Record of Rule Changes Since the 2023-24 Reform}}, year = {2026}, publisher = {Zenodo}, doi = {10.5281/zenodo.22753341}, url = {https://doi.org/10.5281/zenodo.22753341}, note = {Dataset. Licensed CC BY 4.0} }
Cite the DOI above when you need a fixed version that won't change under you. 10.5281/zenodo.22753340 always resolves to the latest Zenodo version. Author ORCID: 0009-0008-0368-4408.
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.
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