In 2026, the UK R&D landscape has a very different “risk profile” from even a few years ago. Not because the definition of R&D has radically changed overnight, but because the admin and compliance architecture around claiming has matured fast: advance notification, mandatory digital forms, tighter scrutiny on who’s doing the work (and where) and sharper rules on contracted activity post-April 2024.

Here are the 10 pitfalls we see most often and why they’re so costly.

If your accounting period begins on/after 1 April 2023, many companies must file a Claim Notification form within six months of the period end before they can claim, especially if they’re a first-time claimant or haven’t claimed recently. Miss it, and you can be shut out of relief for that period.

This isn’t a technical R&D question; it’s a governance one. If your finance function can’t reliably hit notification windows, the “best” R&D work in the world doesn’t matter.

Since 8 August 2023, an Additional Information Form (AIF) has been required to support claims. Errors, omissions or filing it incorrectly relative to the return can lead to rejection, and if you’re close to amendment deadlines, that’s where pain becomes permanent.

Reality check: many failed claims now fail on process, not science.

In 2026, you’re often dealing with:

• legacy SME/RDEC rules for older periods,
• the merged scheme for periods beginning on/after 1 April 2024, and/or
• enhanced rules for R&D-intensive profiles (where relevant).

Getting the start date wrong by even a day can flip key restrictions (especially around contracting and overseas costs).

HMRC doesn’t pay for “innovation vibes.” The strongest claims read like:

• A competent professional is driving the technical direction
• Uncertainty is specific and evidenced
• Attempts and failures are documented
• Advancements are against a baseline, not against your competitor.

Vague language (“we developed a new platform”, “we improved performance”) is the fastest route to enquiry fuel.

AI trap: AI can help structure drafts, but it’s still notoriously weak at context, baseline, and nuance, exactly the things that determine whether your work is R&D or just decent engineering.

A product can be new to your business and still not be R&D. A project can be hard and still not be R&D. The dividing line is usually: did you face genuine scientific/technological uncertainty that couldn’t be readily resolved by a competent professional?

The pitfall isn’t just rejection, it’s credibility damage. If HMRC forms a view that you “claim everything”, every future claim becomes harder.

Contracting is one of the biggest 2026 danger zones.

Under the reformed approach for periods beginning on/after 1 April 2024, entitlement is designed to follow the party making the decision to do R&D and bearing the risk and the rules on contracted-out R&D were significantly reshaped.

Common failure modes:

• Claiming subcontractor costs where you don’t meet the “right to claim” tests
• Misunderstanding who is the “decision-maker” vs who is simply delivering work
• Missing connected-party nuances.

For periods beginning on/after 1 April 2024, relief is generally restricted for overseas subcontracted R&D and overseas EPWs, with limited exceptions where activities necessarily take place abroad.

2026 reality: “Our dev teams overseas” is no longer a footnote; it’s often a structural eligibility problem.

Even where projects qualify, the numbers can kill you.

Classic issues:

• Staff time apportionment based on guesswork rather than evidence
• Including routine QA, support, BAU releases or training as “R&D time”
• Software/cloud/consumables misclassification
• Sloppy allocation methods that don’t reconcile to payroll/GL reality.

If you can’t defend the method, the figure is just a hope with a number attached.

The rules here have changed materially with reforms. For example, government commentary on the merged scheme notes that certain SME subsidy concepts were not carried across in the same way.

The pitfall is assuming:

• “We got a grant, so we can’t claim anything” (often wrong), or
• “We got a grant, and it changes nothing” (also often wrong, depending on facts and scheme/period).

You need to map funding streams to cost lines and periods, not just mention them.

R&D claims are now tightly process-driven:

• Notification windows
• Digital form requirements
• Return amendment deadlines
• The practical reality that HMRC queries often arrive when the people who knew the details have moved on.

The pitfall isn’t just “we missed the deadline.” It’s, we can’t reconstruct the truth six or twelve months later, and that’s when good projects become bad claims.

In 2026, the difference between a robust R&D claim and a risky one is rarely “Did you do R&D?”

It’s more often:

• Can you prove you did it?
• Did you claim it under the right rules for the right period?
• Can you show who decided, who bore the risk and where the work happened?

And that’s why the best R&D advisors now behave less like copywriters and more like quality assurance teams: evidence-led, methodical and allergic to assumptions.