Call CGU and insure the property with them. Make sure you have CONTENTS cover as well. This will cover things like carpets and other fixtures and fittings not included with just insuring the building. Disclose that you have sold the property on a vendor terms contract from the beginning and it would help if you take photos of the property as well if you ever need to make a claim in the future.
There's one other company that insures wrapped properties, however, the premiums cost 30% more and the excess is 5 times the amount CGU charge for a malicious damage claim.