I need to dig out the original agreements and read them through closely but surely this isn't legal?
It is, if you were stupid enough to sign an agreement to that effect without reading the whole thing in full and very carefully.
The music business is all about contracts and personal relationships. If you cannot master those two fields, don't leave the house! Lawyers only help themselves; sometimes the better ones help their clients as a by-product. Understanding contract law is something you can only do for yourself. It's like masturbation: yes, you can get someone to do it for you, but the reality is that most of the time, you have to do it yourself.