Claiming Relief on Pension Contributions

Hi all.

Can anyone help or advise regarding claiming Pension contributions when you have more than the allowance for the year in question.

If no contributions had been made in the last three years and then £150K was made in the 2011/12 tax year. How would you report this in the tax return.

I.e.  You have 2 lots of £50K  Allowance B/Fwd . Do you carry back the contributions and adjust the previous tax returns or do you use the whole £150K in the current  Tax year against the Income  for 2012.

I can't seem to find anything regarding any 'Carry Back' of pension contributions to relieve against the unused pension contributions .

Any help or if anyone can point towards any guidance would be much appreciated.

Thank you.