Sorry, I should have researched this better. Right thought, wrong word: I almost remembered it correctly. Replace omission with "silly error" (no disrespect to OP). I was thinking of CH83143 http://www.hmrc.gov.uk/manuals/chmanual/CH83143.htm which says that a penalty relating to a very straightforward mistake (but still careless behaviour) cannot be suspended. Examples 4 & 5 relate to this, being:I agree with all of your post apart from the first sentence!AKHMRC won't suspend a penalty relating to an omission.
4. Termination payment (paid after P45) omitted.
5. Entering net pay instead of tax deducted.
Given that the OP's circumstances appear to match example 4, I can't see that there is much chance of success in arguing for suspension of the penalty.
