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HMRC internal manual

Stamp Duty Land Tax Manual

Scope: When is Stamp Duty Land Tax (SDLT) chargeable: Contracts and substantial performance: Substantially performed and later completed FA03/S44(8)

Where a contract that has been charged to SDLT by virtue of being substantially performed is subsequently completed by a conveyance both the contract and the transaction effected on completion are notifiable transactions.

However, the tax is due on the latter transaction only to the extent, if any, that the amount of tax chargeable on it is greater than the amount of tax chargeable on the contract.