You could place a restriction on the register of the title preventing them from any dealing until the restriction has been dealt with. You will need a Form RX1 (which you can download from the landregistry website) and will need to file this at HM Land registry along with the appropriate fee.
If you have a mortgage on the property, you will need to redeem this before transferring.
You may also need to consider any stamp duty liability if you are transferring for a consideration.
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