Yes you can. If the property is held in a joint tenancy simply send a letter to your ex unilaterally severing the joint tenancy. This will have the effect of transferring your shares to a 50/50 tenancy in common, which your ex cannot oppose. Notify your local District Land Registry Office of the change on their Form RX 1, it can be printed off from the Land Registry website. There is no fee. You can then do whatever you like with your half share, it requires no one's consent.