There really isn't anything anyone can do now about this situation, IMO. Except let it go, and learn from it.

The lesson to be learned: musicians, get professional legal advice before you sign anything.

Again, IMO, anyone who suggests something can be done about CM/DB is either ignorant of UK law in these matters, or out for vengeance.

There is quite a number of latter inhabiting the UK folk music Internet forums, BTW.