SolvedCH146470 | Interest: repayment interest: special provisions for VAT: common period rule for VAT
From HM Revenue & Customs · Compliance Handbook
You must check whether, and from which date, the FA 2009 interest rules apply to the tax or duty you are dealing with. See CH140160 for full details.
A special provision creates a ‘common period’ for VAT where for any period of time when there are two amounts (either of VAT, or payable in respect of VAT) and;
the amount due and payable by a person carries late payment interest (the overdue payment), and
the other amount payable by HMRC to the person carries repayment interest (the relevant amount)
During the common period late payment interest or repayment interest will accrue only on the remainder/residual amount after the relevant amount and overdue payment are set off against each other.
The common period can be for different accounting periods or the same accounting period.