Hi Henry Lindsay smith,
Please use the Self Assessment criteria tool to confirm that you no longer need to complete self assessment tax returns.
Check if you need to send a Self Assessment tax return
If you determine the answer is no, then you should contact the Self Assessment helpline:
Self Assessment: general enquiries
Or in writing to HMRC BX9 1AS.
We will be able to update your tax record to make Self Assessment dormant.
Self Assessment can be re-activate at a later date if your circumstances change.
Thank you.