Appendix 1: Old Error or Mistake Relief: Is To Be Given in Terms of Tax
From 1 April 2010, it is not possible to make a claim for the old error or mistake relief for any period. The relief is replaced by overpayment relief, see SACM12000+. You will only need the guidance in SACM Appendix 1 if you are dealing with a claim made before 1 April 2010.
The error or mistake in a return provisions do not remove the prohibitions in TMA70/S29 (6), TMA70/S46 (2), and FA98/SCH18/PARA47 (2) which prevent an assessment which has become final from being amended.
Notwithstanding that the relief due is computed as if the error or mistake had resulted in an amendment to an amount assessed, the gross or net assessment in question must not be amended.
Statutorily effect should be given to the relief wholly in terms of tax (but see SACM20070).