HMRC s29 TMA assessments

Client has received a letter (dated 20 June 2012) from HMRC stating that they believe that the 09/10 ITR is wrong because of untaxed bank interest missing from original return. Original return was submitted 30 July 2010 and so HMRC are out of time to make an 'enquiry' into the return. What about discovery assessments?

 

As it happens, the original tax return had included the value of this interest on (paid by a Barclays account), but the taxpayer had thought that this was taxed interest and so had also grossed up the interest and included an amount of 20% tax as 'paid at source'.

 

I have no concerns about this being an 'innocent' error but I wonder whether we can challenge HMRC to even make the discovery at this stage?