Undue delay: the allowable period
The allowable period is the length of time within which HMRC must authorise a claim for repayment, or drawback of excise duty otherwise statutory interest must be paid to the claimant. The allowable period is 30 calendar days, starting with the day on which the claim for repayment or drawback is received.
In practice this means that if HMRC fail to authorise the claim within the 30 calendar days from the date it is received statutory interest must be paid to the taxpayer and there is no requirement for an interest claim to be submitted.
The 30 days cannot be stopped or suspended in any way, however any delays beyond HMRC’s control occurring during the allowable period of 30 days can be excluded when determining the applicable period for statutory interest, see ESIM3400.
Paragraph 4 schedule 3 FA 2001