This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Self Assessment Claims Manual

Consequential Claims after Assessment and Amendment: Claims or Elections Made under Extra-Statutory Concessions

You should follow the same approach to claims and elections made under extra-statutory concessions as you do to those made under the Taxes Acts.

See SACM9030 for further information about out-of-time farmers’ averaging claims