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HMRC internal manual

VAT Default Interest Manual

When to inhibit, amend or withdraw interest: Actual issue date is after issue date on VISION

Where the issue date on a VAT 645 acceptance form has been keyed but the assessment is not issued until a later date, the taxpayer will not have had the full 30 days in which to pay the assessment and avoid further interest. 

VAT 645s must show the same date as that on which the assessment was date stamped and issued.

Where this has not happened and payment has been made within 30 days of the actual issue date, an adjustment to the interest bearing tax may need to be made using Form VAT663, see VDIM6000.