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HMRC internal manual

Appeals reviews and tribunals guidance

Reviews and appeals for direct taxes: Payment of tax pending the outcome of an appeal: Postponement - interest on tax paid late and SA surcharge

Interest is payable on tax and Class 4 NIC paid late, including tax and Class 4 NIC that have been postponed.

So it is important that the decision maker tells the customer of the possible outcome of not making a realistic payment, or any payment, when they appeal against a decision or assessment.

The notes we send to customers with returns and notices of assessment all carry interest warnings so that the customer is aware that interest, where due, will be charged on late payment.