An aspect enquiry is HMRC’s internal label for a compliance check into one or more specific entries on a tax return; a full enquiry examines the return as a whole. Legally there is no difference: HMRC’s own guidance is that every enquiry into a return is an enquiry into the full return, and HMRC staff are told not to use either term when writing to taxpayers. What matters in practice is the scope of the questions in the opening letter, and that scope can widen.
The two labels, and why you will not see them in your letter
HMRC’s Enquiry Manual describes full enquiries as covering “the return as a whole” and aspect enquiries as dealing with “one or more matter(s)”. The same manual tells officers that “all enquiries into tax returns are legally enquiries into the full return” and instructs them not to refer to aspect or full enquiries in communications with the taxpayer or their agent. So the opening letter will simply say HMRC intends to enquire into your return, and will list the information it wants.
What is an aspect enquiry?
An aspect enquiry is a check into specific entries: a single figure that looks out of line, a claimed relief, a property disposal, an expense category. Most enquiries are risk-based selections, driven by something in the return or in the data HMRC holds against it, though some are selected at random. Aspect enquiries are usually shorter and narrower, and many close with no adjustment or a modest one.
What is a full enquiry?
A full enquiry reviews the whole return, and for a business that typically means the underlying records: bank statements, sales and purchase records, and the private side where relevant. Full enquiries take longer, cost more in professional time, and signal that HMRC’s risk assessment has flagged something more fundamental than a single entry.
Can an aspect enquiry turn into a full enquiry?
Yes, and this is the practical consequence of the legal position above. Because every enquiry is legally into the whole return, HMRC does not need any new notice to widen its questions beyond the entry it started with. If the answers to a narrow question raise wider doubts, the check broadens. That is a good reason to take even a single-issue letter seriously and answer it precisely.
How long does HMRC have to open an enquiry?
Under section 9A of the Taxes Management Act 1970, HMRC can enquire into a return filed on time for up to 12 months from the date the return is delivered. For late-filed returns, the window runs to the quarter day (31 January, 30 April, 31 July or 31 October) following the first anniversary of the date the return was delivered. The same time limits apply to amendments. HMRC does not have to give a reason for opening an enquiry; the only condition is written notice, and only one notice of enquiry may be issued for any return or amendment. Once the window has closed, HMRC can generally only go back by making a discovery assessment, which has its own conditions.
What should I do when the opening letter arrives?
Send it to your accountant before responding. The scope of the first reply matters: answering the question asked, accurately and completely, without volunteering the rest of your affairs, is a skill. If HMRC asks for documents beyond what is reasonably required for the check, that can be challenged; formal requests come under Schedule 36, which carries appeal rights.
The cost difference is the real difference
A narrow aspect check might be dealt with in a few letters. A full enquiry into a business return routinely runs into thousands of pounds of professional fees even where the outcome is no additional tax. That fee risk, rather than the label, is what tax investigation insurance exists for: the accountant defends the client’s position fully, and the policy pays the fees. Ask your accountant whether their practice runs a fee protection scheme, see how accountants’ fees in an enquiry normally fall, or get a quote.