If Revenue issued you with a form P12 and asked you to complete and return it then you are obliged to do this as far as I know. Notwithstanding that, to claim tax relief on pension contributions should not, in itself, require a form P12 to be completed and returned. Just write to Revenue including details of the payment (e.g. the PRSA1 certificate for the one off lump sum payment), a copy of your 2003 P60 and details of what you are claiming and they should process it and issue a refund. That's always worked for me anyway.