CH205320 | How to do a compliance check: types of compliance checks: pre-return checks: when they can be done

From HM Revenue & Customs · Compliance Handbook

You may need to carry out pre-return checks in the following circumstances

to assist with pre and post-transaction ruling requests, including some clearances other than non-statutory clearances (but see INTM480000 if you deal with requests for advice on the operation of the transfer pricing rules)
where a person regularly discloses an error (makes a voluntary disclosure) after the submission of a VAT return
checking the hidden economy where waiting for the submission of an SA return may mean unacceptable delay
where you are following up a previous check where poor record-keeping has previously been identified, for example, where an inaccuracy penalty has been suspended
to check the computer systems operated by the person to ensure that the way in which information is kept will lead to accurate returns being made
to find out about tax planning and avoidance schemes, see CH205330
where fraud is suspected.

A risk must be identified before you carry out a pre-return check, unless the person has invited you to make the check.

Inconvenience to the person should be balanced against potential future loss of revenue and advantages gained in terms of education and improvements in record-keeping.

CH205350 covers what to do when you find inaccuracies during a pre-return check.