Its established law that the enquiry window for SDLT is 9 months and 30 days after the filing date. However, we are constantly asked the same question by clients and solicitors alike and that is, under what circumstances does the period extend to 6 years ? Our response is to say that if HMRC discover any materiel fact which they could not have expected to know or were aware of during the 9 month and 30 day window, then they have a right to go into the 6 year perio. But could you perhapd give us 2 examples of these ‘facts’.
Tony, SP1/06 (which also applies to SDLT) is probably the best place to look and that gives some examples. In the SDLT context these would include:
1) informing HMRC that a different view of the law has been taken from theirs especially where a scheme has been used (Pattullo  STC 107 suggests that you should actually tell HMRC that you have done a scheme); and
2) where a market value charge is in point the basis of valuation, details of valuer, whether he was independent etc should be stated.
HMRC seem to be more likely these days to argue that the return was also negligent which means that their ability to assess late is unaffected by the taxpayer’s disclosures (see Hankinson  STC 2640).