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HMRC internal manual

Debt Management and Banking Manual

Irregular Payments: Self Assessment: Set off against SA received in DMB Banking

Where a CODA or exceptionally COP overpayment is to be set off against an SA liability use the SA function CREATE FREESTANDING CREDIT to enter a credit on the SA record.

If you receive a payable order to make the offset you should return it to the issuing office and draw attention to the above instruction.