Non compliance court order mortgage release

[Geronimo]

I had a clean break court order in which part of my exes responibility was to release me from a mortgage on a second property which I entered into under some duress.Some 4 years later he has not done this but has continued to meet payments on the interest only mortgage,so the BS are happy. This is hanging over my head as on paper he is penny less and the property is in negative equity. He continues to use/ rent out the apartment. If he walks away the BS come to me for any outstanding debt which risks my small family home for my two children,he has threatened this and is quite capable of such. Unfortunately the phrase " best endeavours " is included in the court order,I couldn't afford good advice at the time.Is there any way I can force the compliance of the order,ie release me from the mortgage. The BS say he can't afford to remortgage. Is only " known" asset is his pension pot available this year, can I bring this into the issue.