GOV.UK
Examinations: Information: Time limits for opening examinations
a. S14
There is no time limit for opening an examination under S14, although in practice customer service considerations will mean that any S14 action will need to be taken soon after receipt of the claim.
If a retrospective claim is made after the end of the year, you will still be able to open a S14 examination even though that year is now closed. For example, if a claimant makes a claim on 10/4/2009 for tax credit to be backdated to 10/1/2009 you can open a S14 examination before the initial decision is made.
b. S15
There is no time limit for opening an examination under S15. If a change of circumstance, which may increase the maximum rate, is notified after the end of the year, you will still be able to open a S15 examination, even though the year is now closed.
c. S16
S16 examinations cannot be opened until a S14 or 15 decision has been made and the examination must be opened during the year to which the award relates: S16(1) refers to “any time during the period for which an award of a tax credit is made…”. You will therefore be unable to open an examination into a claim which was made during the year if you have not done so by 5th April. You will however be able to open an enquiry, if appropriate, once the S18 decision has been made. (See CCM Chapter 12, CCM12000).