HMRC says that many of the 2020/21 self-assessment tax returns it’s received either include entries for SEISS payments that don’t match the figures it has on record or show nothing at all. As a result, it’s automatically amending those returns and sending out corrected tax calculations. 

Taxpayers should of course check HMRC’s amended figures to make sure they reflect only the total of the first, second or third SEISS grants received on or before 5 April 2021. But that’s not all. They should also check that theyreported the SEISS payments in the right box on the tax return. HMRC’s latest guidance instructs where the payments should be shown.  

If figures have been entered in the wrong place HMRC will assume the taxpayer hasn’t declared the payments at all. It will automatically add them which will result in the individual being taxed twice on the SEISS payments. To avoid this double taxation, an amended tax return should be submitted, reporting the SEISS figures in the right place and removing them from the part of the tax return where they were originally included.