HMRC Tax Enquiries: What Triggers Them, What to Do When the Letter Arrives, and How Penalties Really Work
A brown envelope with HMRC's logo on it has a way of ruining an otherwise good morning. For business owners, landlords, directors and the self-employed, an enquiry letter is one of the few pieces of post that genuinely warrants stopping what you're doing and reading it properly.
The good news is that an enquiry is not an accusation. HMRC opens thousands every year, many of which close with no changes at all. The outcome - and how stressful the process is - depends almost entirely on what happens in the first few weeks: understanding what type of enquiry you're dealing with, knowing your rights, and responding in the right way.
Why This Matters
The size of any penalty depends not on the size of the error, but on the behaviour that led to it. A full, early, well-evidenced response can be the difference between no penalty at all and one approaching 100% of the tax involved.
The main types of HMRC enquiry
HMRC has a range of enquiry types, each with its own scope and statutory basis. Knowing which one you're facing shapes everything that follows.
Aspect enquiries
The most common type. HMRC's risk-profiling flags one specific item - an expense claim, a capital gain, a VAT input tax recovery, or a figure that doesn't match data held elsewhere. Narrow in scope and often resolved quickly with the right records.
s.9A TMA 1970 (individuals/trusts), s.12AC TMA 1970 (partnerships), para 24 Sch 18 FA 1998 (companies)
Full enquiries
Broader, covering the entire return - all income, reliefs and deductions. Opened where several figures look inconsistent, where an aspect enquiry uncovers wider concerns, or where the return forms part of a linked review. The power is identical; only the scope differs.
Same powers as aspect enquiries - the difference is scope, not the provision used
Random enquiries
A small but real proportion of cases with no specific risk flag. HMRC maintains a baseline level of checking to support the integrity of self-assessment. The selection method differs, not the legal basis.
Same statutory provisions as any other enquiry
Employer compliance checks
Focus on payroll, PAYE and NIC - including how benefits in kind are reported on P11Ds and whether employment status is correctly applied. With the Secondary Threshold frozen, errors compound across every employee and pay period.
Sch 36 FA 2008; Reg 80 PAYE Regs 2003; s.8 SSC(TF)A 1999
VAT inspections
Desk-based or in person, typically examining input tax recovery, partial exemption, and the VAT liability of particular supplies. Time-limited rate changes (such as the temporary 5% rate from 25 June to 1 September 2026) create coding errors now and enquiry activity later.
Sch 36 FA 2008 powers; assessments under s.73 VAT Act 1994
IR35 & off-payroll reviews
Check whether status determinations for contractors are correct - especially important for medium and large engagers, who carry the liability if a determination is wrong.
Ch 8 & Ch 10, Part 2 ITEPA 2003; enquiries via standard income/corporation tax powers
R&D tax relief enquiries
Now significantly more common. A much higher proportion of claims face compliance checks, and additional information requirements mean some claims are challenged before they are even processed. Expect more scrutiny, not less.
para 24 Sch 18 FA 1998; Part 13 CTA 2009 as amended by F(No.2)A 2023
CGT & property enquiries
Increasingly data-driven. HMRC cross-references Land Registry records, the 60-day CGT reporting regime, and SDLT filings, making a missing or mismatched disposal an easy and obvious flag.
s.9A TMA 1970; Sch 2 FA 2019 for 60-day returns
Code of Practice 8 (COP8)
Used where HMRC suspects tax avoidance involving complex or substantial sums, but with no allegation of fraud. Handled by the Fraud Investigation Service and typically a detailed, technical dispute about the law.
Operational framework using s.9A TMA 1970 / para 24 Sch 18 FA 1998 plus Sch 36 FA 2008
Code of Practice 9 (COP9)
Reserved for suspected serious fraud. It comes with the Contractual Disclosure Facility - a 60-day window to admit deliberate conduct in return for HMRC not pursuing a criminal investigation. Get specialist advice immediately, before responding at all.
Existing enquiry/information powers; CDF under HMRC discretion (CRCA 2005)
Discovery assessments
Not strictly enquiries, but they sit alongside them. If HMRC discovers an under-declaration outside the normal window, it can assess back four years (innocent error), six years (careless), or twenty years (deliberate).
s.29 TMA 1970; time limits s.34 & s.36 TMA 1970; Sch 18 FA 1998 for companies
What actually triggers an enquiry
HMRC doesn't open enquiries at random in most cases - there's usually a data mismatch or a pattern that stands out. None of these guarantee an enquiry, and none are evidence of wrongdoing on their own, but each increases the statistical likelihood that a return gets a closer look.
- Figures that don't align with data HMRC already holds (via its Connect system - bank interest, dividends, and platform sales from Airbnb, eBay and Etsy)
- Figures well outside the norm for a business of that size and sector
- Repeated use of round numbers or estimates
- A sharp change in profitability from one year to the next
- Sustained losses sitting oddly against an apparently comfortable lifestyle
- Large one-off transactions - a property sale, a substantial director's loan, a sizeable R&D claim
- Returns that have been amended more than once
The letter has arrived: what to do first
The instinct to either panic or ignore it are both unhelpful. A more useful sequence looks like this:
Confirm it's genuine
Enquiry notices arrive by post on official HMRC letterhead - never by text or email asking for bank details, a 'refund', or immediate payment. Those are scams.
Work out what's being checked
Is it an aspect enquiry into one figure, or a full enquiry into the whole return? Which tax year or accounting period does it cover? The notice should specify this - if not, clarify it first.
Check the enquiry window
For a return filed on time, HMRC generally has until the first anniversary of the actual filing date to open an enquiry. Late returns extend that window. An enquiry opened outside it is a significant point worth raising.
Gather records before responding
Bank statements, invoices, contracts, valuations - whatever supports the figure queried. Responding from memory, or guessing to 'move things along', is a common way a simple enquiry becomes complicated.
Get advice early
Particularly for full enquiries, anything referencing COP8 or COP9, or anything where deliberate behaviour might be suggested. The earlier an adviser is involved, the more options remain open.
Manage the deadline
HMRC typically allows around 30 days. If you genuinely need more time, ask for an extension in writing before the deadline - a missed deadline with no explanation looks careless in itself.
Remember meetings aren't compulsory
You can decline a face-to-face meeting and deal with the enquiry entirely in writing, giving more time to consider responses and creating a clear paper trail.
One principle to hold onto
Answer what's been asked, supported by evidence, without volunteering additional information about unrelated matters. That's not about being uncooperative - it's about not inadvertently opening a second front in an enquiry that didn't need one.
How HMRC categorises behaviour - and why it's the whole game
When HMRC finds that tax has been underpaid, the size of any penalty depends not on the size of the error itself, but on the behaviour that led to it. The framework is set out in Schedule 24, Finance Act 2007, and there are four categories. The gap between the bottom of one band and the top of the next is enormous - which is exactly why the behaviour finding dominates how an enquiry is conducted and resolved.
Reasonable care
No penaltyA genuine mistake made despite taking proper care. Tax and interest are still due, but no penalty applies.
Careless
0% – 30%A failure to take reasonable care.
Deliberate, not concealed
20% – 70%The person knew the return was wrong but didn't take steps to hide it.
Deliberate & concealed
30% – 100%Active steps were taken to hide the inaccuracy.
Disclosure reduces the penalty - sometimes a lot
Within each band, the actual percentage charged depends heavily on how and when the inaccuracy is disclosed. An unprompted disclosure - made before there was any indication HMRC was checking - earns the largest possible reduction within the band. A prompted disclosure, made after HMRC has started asking questions, still earns a reduction, but a smaller one.
The quality of the disclosure also matters: HMRC assesses this on the basis of "telling, helping and giving access" - being upfront about what went wrong, helping HMRC understand the figures, and giving access to the records needed to check them. A full, early, well-evidenced disclosure can move a penalty from the top of a band to close to its floor.
Suspended penalties - a second chance
For careless inaccuracies specifically, HMRC can suspend a penalty for up to two years, subject to conditions aimed at preventing the same error happening again - a new bookkeeping process, for example, or professional help with a particular area of the return. If the conditions are met for the full period, the penalty is cancelled entirely. This option isn't available for deliberate behaviour.
Other penalties in the background
A few related regimes are worth being aware of even if they're not the main event in most enquiries.
Failure to notify penalties apply where someone should have registered for a tax (such as VAT or self-assessment) and didn't, using a similar behaviour-based structure - set out in Schedule 41, Finance Act 2008.
Offshore penalties can be significantly higher - Schedule 24 itself increases the standard penalty for "offshore matters" and "offshore transfers", and a separate asset-based penalty under Schedule 22, Finance Act 2016 can apply on top where the non-compliance was deliberate.
Late filing and late payment penalties apply automatically based on timing alone, regardless of behaviour, under Schedule 55 and Schedule 56, Finance Act 2009 respectively.
If you don't agree with HMRC's conclusion
Disagreement doesn't have to mean a tribunal straight away. The right of appeal against most HMRC decisions comes from section 31, TMA 1970 (with equivalent provision for companies in Schedule 18, FA 1998), and there's a 30-day window to use it.
Statutory review
An internal review by a different HMRC officer under sections 49A to 49I, TMA 1970 - often resolves matters without further escalation.
Alternative Dispute Resolution
A mediated route that can run alongside an open enquiry, bringing in an independent facilitator to help both sides reach agreement.
First-tier Tribunal
Where none of that resolves things, the Tribunal provides an independent route to a binding decision.
The practical takeaway
Most enquiries are resolvable without drama - but resolvable depends on records being in order, responses being accurate and evidenced, and advice being sought before anything is said in writing that's hard to walk back. For anyone wanting more certainty before a position is even taken, HMRC's new Advance Tax Certainty Service, launching 1 July 2026, offers a way to get a view in advance rather than defend a position after the fact.
If an enquiry letter has landed on your desk, the worst response is no response - and the second worst is a rushed one. Get the facts together, understand exactly what's being asked, and get advice early enough that it actually changes the outcome.
Received an Enquiry Letter from HMRC?
Our team handles HMRC enquiries from first letter to final resolution - protecting your position, managing correspondence, and working to keep any penalty to the absolute minimum. The earlier we're involved, the more options remain open.
Key Takeaways
- An enquiry is not an accusation - many close with no changes at all
- Most enquiries are triggered by data mismatches via HMRC's Connect system, not random chance
- Confirm the letter is genuine, check the enquiry window, gather records, and get advice early
- Penalties depend on behaviour (Schedule 24, FA 2007) - from no penalty for reasonable care to 100% for deliberate and concealed conduct
- Early, unprompted, well-evidenced disclosure can dramatically reduce any penalty
- A COP9 letter requires specialist advice immediately, before responding to HMRC at all
This article provides general guidance on UK tax enquiries and does not constitute advice for any specific situation. If you've received an enquiry letter from HMRC, speak to a tax adviser before responding.