The general rule for employees’ expenses: dealing with expenses: how to resolve a dispute: years for which assessments have become final and conclusive
Where a self assessment for any year has become final, the only way that a deduction can be permitted is by a claim under Schedule 1AB TMA 1970.
This is a claim that can be made by any person who has been overcharged in an assessment. An overpayment relief claim can be made for an omission from a return, such as forgetting to include an allowable expense, but not for forgetting to include a claim in a return. SACM 2005 and 2010 explain what “claim” means for this purpose.
Guidance on the time limit within which an error or mistake relief claim must be made, together with guidance on how to deal with a claim is at SACM12000.