Brought Forward Pension Annual Allowances

Hoping for some clarification

Under the new rules, where an individuals pension contributions are sufficient that the remaining 50K of allowances from the previous 3 tax years can be brought forward to 11/12, how do i disclose this on the 11/12 tax return?

There doesnt appear to be anywhere other than this being a white space discloure? If it is even required at all? Given the amount of tax at stake by claiming such relief, I had assumed that HMRC would have put this on a supplementary page somewhere?

Can anyone please help?

Thanks