Receiving a letter from HMRC opening an enquiry into your Self Assessment return is unsettling. Understanding what is happening and what your rights and obligations are, is the first step to resolving it efficiently and on the best possible terms.
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What a Self Assessment enquiry is
A Self Assessment enquiry is HMRC’s formal investigation into a submitted tax return. The legal basis for opening an enquiry into an individual’s or sole trader’s return is section 9A of the Taxes Management Act 1970 (TMA 1970). For partnership returns, the equivalent power is section 12AC TMA 1970.
HMRC opens an enquiry by giving written notice to the taxpayer. The notice must be given within the statutory window (see below). It must state whether HMRC is conducting an aspect enquiry or a full enquiry into the return. The notice triggers a series of rights and obligations on both sides.
An enquiry is not the same as an accusation of fraud. It is HMRC exercising its statutory right to verify that the return is correct. The vast majority of enquiries are resolved by correspondence and document exchange without any finding of serious wrongdoing.
How HMRC selects returns for enquiry
HMRC uses several mechanisms to identify returns that warrant examination.
HMRC Connect risk-scoring
Connect is HMRC’s data analytics platform, holding over 30 billion data points. It cross-references the figures in your return against third-party data sources including: employer PAYE returns, bank interest data, Land Registry transactions, letting agent reports, Companies House filings, social media profiles and Common Reporting Standard data from over 100 overseas tax authorities. Where your return appears inconsistent with the external data, Connect flags the return as higher risk.
Random sample selection
Every return faces a small but real risk of random selection, regardless of how accurate it is. HMRC uses random enquiries partly to gather intelligence about compliance levels across different taxpayer populations and partly to act as a deterrent.
Specific risk indicators
Certain patterns in a return reliably attract HMRC attention:
- Large or unusual expense claims relative to turnover
- Fluctuating income from year to year without an obvious commercial explanation
- A first return after starting a business or becoming self-employed
- Offshore income, foreign assets or foreign bank accounts
- Rental losses claimed against other income
- Transactions between connected parties (e.g. family members)
- Capital gains calculations on property or business disposals
Prior year findings
If a previous enquiry uncovered errors or underpaid tax, HMRC may return to check whether the same issues recur in later years. A prior enquiry that found carelessness raises HMRC’s appetite to look again.
Aspect vs full enquiry
One of the most important things to identify when you receive an enquiry notice is whether HMRC has opened an aspect enquiry or a full enquiry. The distinction affects the scope of HMRC’s information requests and your obligations.
An aspect enquiry is limited to one or more specific items in the return, for example, self-employment expenses or rental income from a specific property. HMRC’s information requests must be confined to those aspects, and you are not obliged to provide documents relating to parts of the return not under examination.
A full enquiry examines the entire return and all underlying records. It is used where HMRC suspects more widespread non-compliance or where the taxpayer is flagged as higher risk by Connect. HMRC requires broader disclosure of documents, and the process is generally more demanding.
HMRC must state in the notice which type of enquiry it is opening. If the notice does not make this clear, seek professional advice immediately.
For a detailed comparison, see our guide: HMRC Aspect Enquiry vs Full Enquiry, What’s the Difference?
The enquiry window
HMRC’s power to open an enquiry under s9A TMA 1970 is time-limited. HMRC must give the enquiry notice within 12 months of the date the return was filed (or the date it was due, if filed early).
- If you filed your return on time (by 31 January), HMRC must open the enquiry by 31 January the following year.
- If you filed your return late, say, on 1 April, the enquiry window closes 12 months from that date.
Once the window closes, HMRC cannot open a formal s9A enquiry. Its only route to challenge the return is a discovery assessment under s29 TMA 1970, which is subject to stricter conditions.
One important trap: if you amend your return after filing, HMRC gets a fresh 12-month window to enquire into the amended aspects. This can reopen exposure you thought was time-barred.
See our detailed guide: HMRC Enquiry Window, How Long HMRC Has to Open an Enquiry.
What HMRC can ask for
HMRC’s power to require documents and information during an enquiry derives from Schedule 36 of the Finance Act 2008. A Schedule 36 taxpayer notice (paragraph 1) requires documents and information that are “reasonably required” to check the taxpayer’s tax position.
In a Self Assessment enquiry, HMRC routinely requests:
- Personal and business bank statements
- Sales invoices and purchase receipts
- Contracts with customers and suppliers
- PAYE records (if the taxpayer is also an employer)
- Property purchase and sale documents
- Accounting records: ledgers, cashbooks, till rolls
- Correspondence with advisers (subject to legal professional privilege)
Documents must be provided within the timeframe stated in the Schedule 36 notice. For the full rules on what HMRC can and cannot compel, see: What Documents Must You Give HMRC in a Self-Assessment Enquiry?
You may also find our broader guide on formal information requests useful: HMRC Schedule 36 Information Notices.
Your obligations and their limits
Once HMRC has issued a Schedule 36 notice, you are legally required to provide the documents and information specified, subject to important exceptions:
- Legal professional privilege (LPP): Communications that constitute legal advice from a solicitor or barrister are absolutely protected from disclosure. Paragraph 23 of Schedule 36 FA 2008 preserves LPP. HMRC cannot compel you to disclose the contents of privileged legal advice, even if it is directly relevant to the matters under enquiry.
- Accountant’s working papers: These are not protected by LPP. Accountants do not have the same professional privilege as solicitors. HMRC may request underlying working papers, though in practice its own guidance indicates it will not do so routinely.
- Documents not in your possession or power: You cannot be required to produce what you do not have and cannot reasonably obtain.
- Personal records: Paragraph 24 of Schedule 36 provides limited protection for personal records such as medical or psychiatric information.
Closure notices
Section 28A TMA 1970 requires HMRC to issue a closure notice when it has completed its enquiries. The closure notice must either state that no amendment is required or specify any amendment to the return. The return is then treated as having been made with the amendment stated.
HMRC has no statutory deadline by which it must close. Enquiries can drift on for years, particularly in complex cases. If HMRC is unreasonably delaying, a taxpayer can apply to the First-Tier Tribunal (Tax Chamber) under s28A(4) TMA 1970 for a direction requiring HMRC to close the enquiry within a specified period. The FTT will grant the direction unless HMRC can show “reasonable grounds” for continuing.
Full details of this powerful remedy are in our guide: Forcing HMRC to Close an Enquiry, Closure Notice Applications.
Resolution routes
Most Self Assessment enquiries are resolved in one of three ways:
Settlement by agreement
The most common outcome. You and HMRC agree on any amendments to the return, any underpaid tax, interest and penalties. Agreement is documented in a contract settlement (using HMRC’s standard form). This closes the enquiry without the need for tribunal proceedings.
Alternative Dispute Resolution (ADR)
Where negotiations with the inspector have stalled, ADR offers a facilitated discussion with an independent HMRC mediator. ADR is free to access and often breaks deadlocks. It does not bind either party but frequently leads to settlement.
Statutory appeal to the First-Tier Tribunal
If HMRC issues a closure notice with an amendment you dispute, you have 30 days to appeal to the FTT (Tax Chamber). The FTT hears the evidence and makes binding findings of fact and law. This is the formal litigation route and is appropriate where a point of principle is at stake or where HMRC’s position is simply wrong.
After the enquiry: what happens next
Once the enquiry closes, HMRC will issue any necessary amendment to the return. Several consequences flow from this:
- Additional tax: Any underpaid tax becomes due and payable. Interest accrues from the original due date.
- Penalty assessment: If the enquiry found errors in the return, HMRC will assess a penalty under Schedule 24 FA 2007. The penalty percentage depends on whether the error was careless, deliberate or deliberate-and-concealed and on the quality of the taxpayer’s cooperation.
- Discovery assessments: If the enquiry reveals that other years are also affected, HMRC may raise discovery assessments under s29 TMA 1970 for those years.
- Future returns: A finding against you in an enquiry makes future scrutiny more likely. HMRC’s risk-scoring models note the history of non-compliance.
Frequently asked questions
Does an enquiry notice mean HMRC thinks I’ve done something wrong?
Not necessarily. HMRC selects returns through a combination of risk-scoring and random sampling. A random-selection enquiry means exactly that, your return was drawn at random, not because HMRC suspects wrongdoing. That said, an enquiry triggered by HMRC Connect risk-scoring does indicate that one or more data points have raised a flag. Either way, the process is the same and professional representation is advisable from the outset.
Can HMRC open an enquiry for a previous year?
HMRC can open a formal s9A enquiry only within the 12-month window from the filing date of each year’s return. Once that window closes, HMRC must use a discovery assessment under s29 TMA 1970, which is subject to stricter conditions. If the s9A window is still open for a prior year’s return, HMRC can open a concurrent enquiry into that year as well as the current year.
What happens if I don’t respond to HMRC’s enquiry?
Ignoring an HMRC enquiry is not a viable strategy. HMRC can issue a formal Schedule 36 FA 2008 information notice and non-compliance with such a notice attracts a fixed penalty of £300 plus daily penalties of up to £60 per day. Persistent non-cooperation may lead HMRC to make a best-of-judgement assessment, raise a jeopardy amendment or escalate to a more serious investigation. Prompt, managed engagement is always preferable.
How long does a Self Assessment enquiry take?
A straightforward aspect enquiry targeting a single item can be resolved in three to six months. A full enquiry into a complex return, particularly one involving offshore income, property transactions or substantial business records, can take 12 to 36 months. There is no statutory deadline for HMRC to close an enquiry, but if HMRC is unreasonably delaying, a taxpayer can apply to the First-Tier Tribunal for a direction requiring closure under s28A(4) TMA 1970.
Related guides
- HMRC Enquiry Window, How Long HMRC Has to Open an Enquiry
- HMRC Aspect Enquiry vs Full Enquiry, What’s the Difference?
- Forcing HMRC to Close an Enquiry, Closure Notice Applications
- What Documents Must You Give HMRC in a Self-Assessment Enquiry?
- HMRC Schedule 36 Information Notices
- Income Tax Investigation Service