An HMRC customs audit is a check on whether your import and export declarations were correct and whether you paid the right duty and import VAT. HMRC’s own term is a compliance check, and it usually begins with a letter asking for records — not an unannounced visit.
The important thing to understand up front: a compliance check looks backwards. HMRC can assess underpaid duty across a four-year window, so a check opened today can reach declarations made in 2022. Whatever you fix now does not undo what was declared then.
What triggers a check
There is no published list, and HMRC does not explain its selection. In practice, checks tend to follow from:
- Risk profiling of your declaration data — commodity codes that do not match the goods description, values that sit outside the norm for that code, origin claims that look unlikely
- Inconsistency over time — the same product declared under different codes across months or suppliers
- Special procedures — Inward Processing, Outward Processing, customs warehousing and temporary admission carry ongoing conditions, and HMRC checks whether those conditions were met
- Preference claims — zero duty under a trade agreement depends on evidence you must hold
- A previous error or warning letter
- Sector or route-based campaigns — HMRC periodically focuses on particular goods or trade lanes
- Simply being a large importer — volume alone makes you worth checking
None of these means you have done something wrong. A check is a check.
What HMRC asks for
Broadly: the declaration, and everything behind it. Expect requests covering
- Customs declarations and the MRN for each entry
- Commercial invoices and purchase orders
- Transport documents — bills of lading, air waybills, CMRs
- Evidence of customs value — including freight and insurance costs, royalties, licence fees, tooling and assists
- Proof of origin where preference was claimed
- Licences, permits and certificates — import licences, CITES permits, health and phytosanitary certificates
- Records for any special procedure — including warehousing, Inward Processing and free zone records, and Bills of Discharge
- Your duty and VAT accounting — deferment statements, postponed VAT accounting statements
The rule of thumb: for every figure on a declaration, HMRC can ask what it was based on and to see the document it came from.
The four-year record obligation
You must keep import and export records for four years, and that obligation is yours as the importer regardless of who submitted the declaration. Appointing a broker does not transfer it.
This is where most compliance checks actually go wrong. The declaration itself is usually retrievable — HMRC has it, and you can pull your own copy from HMRC’s Get Customs Data service. What is harder is producing, per MRN, the invoice, the transport document, the valuation basis and the origin proof that together justify what was declared.
If those documents live in four systems, three inboxes and one filing cabinet, a check that should take days takes months — and every week you spend assembling evidence is a week HMRC’s questions remain open.
How a check usually runs
1. The opening letter. HMRC writes setting out what they are checking and what they want. It normally arrives with a factsheet — CC/FS1g, “Compliance checks: customs and international trade” — which explains your rights and what happens next. Read it; it is short and it tells you things the covering letter does not.
2. You provide records. Usually within a stated deadline. If you need longer, ask — HMRC will often agree an extension, and asking is far better than missing the date.
3. Questions and clarification. HMRC may ask why a particular code was used, how a value was calculated, or for evidence behind an origin claim. Answers that are specific and documented close these quickly; answers that are vague generate more questions.
4. A visit, sometimes. Larger or more complex checks may involve a visit to your premises to see systems and records in place.
5. The outcome. Either the check closes with no adjustment, or HMRC issues an assessment for underpaid duty and import VAT, potentially with a penalty. If you have overpaid, that can be reclaimed — normally using form C285 within three years of the customs debt arising.
Penalties: what is actually at stake
Two things get confused here, so it is worth separating them.
The duty assessment is not a penalty. If you underpaid, you owe the difference. That is not a fine — it is the tax you should have paid, and across four years of imports it is usually the largest number in the whole exercise.
Civil penalties are separate and comparatively small. Under the Customs (Contravention of a Relevant Rule) Regulations, penalties for contraventions of customs law generally range from £1,000 to £2,500, and HMRC will normally only charge one after issuing a warning letter first. Notice 301 sets out how these work.
There are time limits on penalties: HMRC must issue one within three years of the contravention, or within two years of becoming aware of facts sufficient to justify it.
Suspected deliberate evasion is a different track entirely. Where HMRC suspects dishonest evasion rather than error, it may proceed under the civil investigation procedure set out in Notice 300. That is a serious matter and the point at which you should be taking professional advice rather than reading an article.
For most importers, though, the realistic exposure is an assessment for underpaid duty across four years plus a penalty in the low thousands — and the assessment is what hurts.
How to be ready before the letter arrives
Preparation is almost entirely about evidence being retrievable, not about being perfect.
1. Know what was declared in your name. Request your own data from HMRC. You cannot check declarations you have never seen.
2. Reconcile declarations against your own records. Does each declaration match a purchase order, an invoice and a goods-received record? Mismatches are where assessments come from.
3. Check classification consistency. Same product, same code, every time. Inconsistency is both a common error and a visible signal that nobody is reviewing.
4. Keep evidence per MRN, not per filing cabinet. The unit HMRC works in is the declaration. If your evidence is organised by supplier or by month, you will be re-assembling it under time pressure.
5. Document your reasoning, not just your paperwork. Why this commodity code? What was the valuation basis? On what evidence was preference claimed? Contemporaneous reasoning is far more persuasive than a reconstruction two years later.
6. Know your representation. Whether you are on direct or indirect representation determines who HMRC pursues for the debt.
7. If you find an error, consider disclosing it. Errors found and voluntarily disclosed are treated more favourably than errors HMRC finds. That is a decision to take advice on, but silence is rarely the better option.
Where this gets hard, and what we do about it
Everything above is achievable manually for a business filing twenty declarations a month. At several hundred a month, across multiple suppliers and commodity codes, the patterns that trigger assessments are effectively invisible in spreadsheets — they only appear when you compare declarations against your own records continuously, over months.
That is what the HC Customs compliance portal does. It pulls your CDS declaration data as an authorised third party, reconciles it against your purchase and goods-received records, flags duty anomalies and inconsistent classification as they happen, and assembles an audit-defence pack per MRN — declaration, invoice, transport document, valuation basis, origin proof — so that when a compliance check letter arrives, producing the evidence is a download rather than a project.
It also identifies duty you have overpaid, which is the part most importers never get round to and the part that pays for itself.
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Frequently asked questions
How far back can HMRC go in a customs audit?
HMRC can assess underpaid customs duty across a four-year window, which is also how long you must keep your import and export records.
Does HMRC warn you before a customs audit?
Usually yes. A compliance check normally begins with a letter setting out what is being checked and what records are needed, accompanied by factsheet CC/FS1g. Unannounced visits are not the norm for routine checks.
What penalties can HMRC charge for customs errors?
Civil penalties for contraventions of customs law generally range from £1,000 to £2,500, and are normally only charged after a warning letter. Separately — and usually far more significant — HMRC will assess any underpaid duty and import VAT. Suspected deliberate evasion follows a different and more serious process under Notice 300.
Am I liable if my customs broker made the mistake?
Under direct representation you are solely liable for the customs debt; under indirect representation you and your agent are jointly and severally liable. Either way, the record-keeping obligation and the assessment normally land on the importer.
What should I do when a compliance check letter arrives?
Read the factsheet, note the deadline, and start assembling records immediately. If the deadline is not realistic, ask for an extension rather than missing it. If you think there may be an underlying error, take advice before responding — how an error is presented materially affects the outcome.
Can I reclaim duty I have overpaid?
Yes, normally using form C285 within three years of the date the customs debt arose. Compliance checks quite often surface overpayments as well as underpayments.