In reply to benky1979:
You and your ex both signed a contact with the lender agreeing that either of you could be chased for the full debt. A contract between you and your ex does not remove her signature form that mortgage contract.
So if you pop your clogs or do a runner she has both a contract saying she doesn't own the house and a contract saying she is liable for the debt. Not good for her.
When you apply in the future for a remortgage in your name only the land registry would will still have her name on it. You won't get the new mortgage in your name only because the land registry says you only own half the property. Not good for you if you've given her the money and she can't be bothered to sign.
I bought my flat in my name only when I was single but when I sold my wife had to sign to give permission and that I wasn't making her homeless. Not good for in your case if you've given her the money and she can't be bothered to sign.
I'd say you need to solicitor, perhaps to do a formal transfer of ownership and you can't do that without the agreement of the lender who has the mortgage registered against the property.
This must a familiar situation for solicitors and lenders.
Post edited at 16:46