HMRC Compliance Check Letter: What it means and how to respond

Key Takeaways: Received an HMRC Tax Compliance Check?

• Don't Panic, But Don't Delay: Compliance checks are common routine audits triggered by automated data matching (e.g. comparing declared income against bank interest, card processors, property sales, or overseas reporting).
• Check the Scope (Aspect vs Full): Identify whether the letter is asking for proof of a single specific expense (Aspect Check) or auditing your entire tax year (Full Enquiry).
• The 30-Day Clock: Note the response deadline on page 1. Missing it without requesting an extension can result in formal information notices (Schedule 36) and statutory £300+ penalties.
• Get Professional Representation: Having a Chartered Tax Adviser (CTA) respond to HMRC on your behalf significantly reduces the risk of penalties and limits the enquiry from expanding into other tax years.

If you received a letter from HM Revenue & Customs titled "Check of your tax return" or "Compliance check", HMRC has formally opened an enquiry into your tax affairs.

What is an HMRC compliance check?

A compliance check is HMRC’s statutory process for verifying that the figures submitted on a Self Assessment, VAT, PAYE, or Corporation Tax return are complete and accurate.

Under UK tax law (specifically Section 9A of the Taxes Management Act 1970 for individuals, and Schedule 18 FA 1998 for companies), HMRC has the statutory right to open an enquiry within 12 months of receiving your tax return.

What triggers an HMRC compliance letter?

Contrary to popular belief, not all checks mean you are suspected of fraud. Common triggers include:

1. Automated Data Matching (Connect System): HMRC's AI system cross-references your return against third-party data from banks, Airbnb/Booking.com, eBay/Etsy/Vinted, Land Registry property transfers, and crypto exchanges.
2. High Expense-to-Income Ratios: Claiming unusually high travel, home office, or motoring expenses compared to industry benchmarks.
3. Fluctuating Turnover or Sudden Losses: Significant drops in profit or unexpected claims for loss relief.
4. Random Selection: A percentage of UK personal and business returns are audited purely at random each year.

Types of HMRC compliance checks

1. Aspect Enquiry (Specific Item)

HMRC only wants clarification or proof regarding one or two specific sections of your return.

• Examples: Asking for proof of foreign dividend withholding tax, capital gains relief on a property sale, or proof of a large charitable donation.

2. Full Enquiry (Entire Return)

HMRC reviews your entire tax return, including all business books, bank accounts, personal expenditure, and accounting records for that tax year.

5 Key stages of an HMRC compliance check

1. Identify the Deadline: Check page 1 for the exact 30-day response date.
2. Review the Information Request Notice: Determine whether HMRC is checking one specific item (Aspect Check) or auditing your full year (Full Enquiry).
3. Gather Supporting Evidence: Collect the corresponding invoices, receipts, and bank statements before preparing any reply.
4. Formulate a Structured Written Response: Answer only the specific questions asked, with clear supporting calculations.
5. Request Written Confirmation of Closure: Obtain a formal HMRC Closure Notice (or negotiated settlement) to conclude the enquiry.

Step 1: Check the caseworker's deadline

Note the date on the letter and the reply deadline. If gathering bank statements or old receipts will take longer than 30 days, contact the caseworker or have your accountant email them to agree on a formal extension.

Step 2: Answer only what is asked

Provide full and truthful answers to the specific points raised in the letter, but do not volunteer unrelated files or speculative commentary. Extra unorganized documents can invite caseworkers to expand the scope into other tax years.

Step 3: Check for reasonable excuse / unprompted disclosures

If you realize an error was genuinely made on the return, making a prompt, cooperative disclosure to HMRC before they point it out significantly reduces or eliminates penalties.

What to gather before asking an expert for help

1. The complete HMRC letter (all pages including the factsheet reference code, e.g. CC/FS1a).
2. The tax return (SA100/CT600) for the year under check.
3. Your supporting invoices, bank statements, or calculation worksheets related to the challenged line items.
4. Any prior correspondence or clearance applications with HMRC.