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HMRC internal manual

Stamp Duty Land Tax Manual

Scope: What is chargeable: Contract and conveyance: Contract and later conveyance

Where a contract that is within the scope of Stamp Duty Land Tax (SDLT) because it is substantially performed before completion is completed by conveyance, that completion must also be notified.

SDLT is due on completion to the extent that the tax due on completion exceeds that due on the contract.