Official error: the applicable period: failure to provide further information
Where verification of the principal claim or the interest claim is delayed because the taxpayer failed to provide information requested by HMRC that period must be ignored when determining the applicable period.
The period to be ignored begins with the day when HMRC request the taxpayer to provide the information considered to be relevant, and ends when they are satisfied there is sufficient evidence to authorise the claim
When issuing a request for further information you may set a reasonable time limit for a response depending on what information is required. You should also warn the taxpayer that any delay in responding will reduce the interest calculation period.
You will need to judge at what point you had sufficient evidence to authorise the claim and determine any period of delay to be deducted. Evidence of delay will need to be strong enough to defend in the event of an appeal.
Paragraph (11) schedule 3 FA 2001