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If the clawback provision is still applicable, there will be a Restriction in the Charges Register of the Land Registry deeds (the official copies) in favour of the person who has the benefit of the clawback.
The wording to the clawback provision will be contained in the Land Registry Transfer document, which would have been signed between the original parties to the agreement. You should be able to obtain a copy from the Land Registry, but to be honest, if there is no Restricition in the Charges Register, I am guessing that the clawback period has expired.
I hope this helps and answers your question.
Please let me know if you require any further clarification.