no one will question where you got the money from if you want to redeem the loan, none of their business. As Monbretia said, the clawback is only applicable if you SELL which has been echoed time and time again on this forum. Also it is only applicable if you sell it ABOVE the price you paid......All property bought during that period will have lost about 50/70% so no fear of that financial instrument kicking in.
What you are doing is REDEEMING the loan before the mortgage term. So for example, if you have 15 years left on the loan you are redeeming early you are STILL bound to the council, "just in case the value goes up" for the remaining period, this will also mean you will not be even allowed to lease out your home that you have fully paid for without their permission which as you know, they dont permit. (bumer eh....)
The only way to sever the link with them is to SELL. So the only idea I can think of is if you have a spouce/partner you can trust and "sell" it to him/her.