Assignable contracts in UK property: how assignment of contract actually works

Assignment of contract means the buyer under a property purchase contract (the assignor) transfers their contractual right to buy to a new buyer (the assignee), who then completes the purchase directly with the original seller. Only the benefit of the contract moves, not the burden, and the original buyer is generally still on the hook if the assignee fails to perform, unless the seller agrees otherwise. It is popular with sourcers because it needs very little capital: you are selling a right to buy, not the property itself, so there is no need to fund a purchase and a resale as two separate transactions.

Check the contract before you rely on this

Not every contract can be assigned. Many standard sale contracts, and most new-build or off-plan developer contracts in particular, include a clause prohibiting assignment or requiring the seller's written consent first. Before building a sourcing strategy around assignment, the specific contract needs checking, not assumed to allow it because other similar deals have in the past.

Legal assignment versus equitable assignment

UK law recognises two forms. A legal assignment must be in writing, must be absolute (not conditional or partial), and requires written notice to the seller, at which point the assignee can enforce the contract directly in their own name. An equitable assignment is more flexible, it can be informal and can cover only part of a right, but it is weaker: the assignee often needs the original buyer to join in or assist to enforce it fully. Sourcers structuring an assignment deal should be clear about which form is being used and should not assume an informal arrangement carries the same legal weight as a written, notified assignment.

Lenders can be wary of reassigned contracts

Mortgage lenders have historically been cautious about funding a purchase where the contract has already been assigned once, and particularly wary of a contract reassigned multiple times, a pattern associated with certain pre-2008 property schemes. An end buyer relying on mortgage finance should confirm with their lender early that an assigned contract will be acceptable, rather than discovering a problem close to completion.

The SDLT treatment: sub-sale relief

Where a buyer assigns their right to a land transaction before it completes, HMRC's sub-sale relief is generally designed to ensure Stamp Duty Land Tax is paid once, by the end transferee who actually acquires the property, rather than twice. This relief (claimed using relief code 34 on the land transaction return) applies to what HMRC calls an assignment of rights, and has conditions attached, including that the original contract must complete or be substantially performed at the same time as, and in connection with, the assignment. Getting this wrong can mean double SDLT exposure, so this is an area worth taking specific tax advice on for anything beyond a straightforward single assignment.

For the wider sourcing and packaging process an assignable contract typically sits inside, see the UK property sourcer playbook and the deal packaging guide.

Common questions

Can you assign any property purchase contract?

No. Many contracts, especially standard developer and off-plan contracts, contain a clause prohibiting assignment or requiring the seller's written consent. The specific contract needs checking before relying on assignment as a strategy.

What is the difference between assignment and double completion?

In an assignment, the original buyer transfers their contractual right to buy to a new buyer, and completion happens once, directly between the original seller and the end buyer. In a double completion (or back-to-back deal), the original buyer actually completes the purchase first, then immediately resells, meaning two separate completions.

Do you pay stamp duty twice on an assigned contract?

Not normally, if the transaction qualifies for HMRC's sub-sale relief, which is designed so SDLT is paid once by the end transferee. This relief has specific timing and documentation conditions, so professional advice is worth taking on anything beyond a simple single assignment.

Will a mortgage lender fund the purchase of an assigned contract?

It depends on the lender and the history of the contract. Lenders are often more cautious about a contract that has already been assigned, and particularly wary of multiple reassignments, so it is worth confirming lender appetite early rather than close to completion.

Legal and tax information verified against multiple UK sources (lexisnexis.co.uk sub-sales and assignments guidance, sprintlaw.co.uk, gov.uk HMRC Stamp Duty Land Tax Manual), August 2026. This is general information, not legal or tax advice; take specific advice before assigning or accepting an assigned contract.