[SACM20040] Appendix 1: Old Error or Mistake Relief: Causal Link
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.
Broadly TMA70/S33 provides relief for a person who has overpaid tax `by reason of some error or mistake in a return'.
There must therefore be a direct causal link between the error in the return and the excessive assessment.