The general rule is that HMRC can open an enquiry into your Return anytime within 12 months after the filing date if the return is filed on or before the deadline.
If the return is late or amended then HMRC have until the quarter day next following the first anniversary of the day on which the return or amendment was made. Quarter days are: 31 January, 30 April, 31 July and 31 October.
After the enquiry window has closed, HMRC can only investigate your return if they can raise a “discovery” assessment. If there is no fraud or negligence the discovery window is 4 years. If there is negligence (carelessness) the window is 6 years. Otherwise it is 20 years.
HMRC can raise a discovery assessment if:
- There is a loss of tax; and,
- The loss of tax was brought about carelessly or deliberately by the taxpayer or a person acting on his behalf; or,
- The time limit for issuing a notice of enquiry into the return passed, or the enquiries were completed, the officer of the Board could not have reasonably been expected, on the basis of the information made available to him, to be aware of the situation mentioned in the first paragraph under this sub-heading above.
The underlined italic has been the subject of a lot of litigation – what do “reasonably expected” and “made available” mean? While the topic is too broad to cover here, in general terms HMR should be reasonably expected to know if there has been a full disclosure on the Return.
If HMRC cannot show this, then they cannot raise a discovery assessment and the taxpayer should have certainty of his tax position after the enquiry window closes.