Hi
Higher rate tax relief is available on the unused allowance from the last 3 year added to the maximum tax free allowance in the tax year.
Tax returns can be amended for up to two years after the due date of the tax return, eg. 22/23 tax return due 31/01/23, so can be amended up to 31/01/25.
For the two previous tax year, an overpayment relief claim (OPR) can be submitted in writing, using the guidance at SACM12150 (
SACM12150 - Overpayment relief: Form of claims).
Please note that an OPR claim for 2019 to 2020 must be in HMRC possession no latge than 5 April 2024. Any claims for 19/20 received after that date, will be out of date and rejected.
Thank you