CG13810 - Claims and elections: late claims and elections: responding to
If the customer has not already done so, they must put the claim or election into any proper form specified for that purpose before it is considered.
Where a claim or election is made under TCGA 1992 or a related Extra Statutory Concession after the time limit or extended time limit as referred to in CG13751 if appropriate, has expired, that fact should be pointed out to the customer.
In certain circumstances a late claim or election under TCGA92 may be accepted locally. The part of this manual for the particular claim or election will tell you if you can do this e.g. see CG60640, CG45357.
In other cases you should follow the guidance within the Self Assessment Claims Manual see SACM10035+.