Are you in an IVA and need to release some just before the end?
If so, you will have to try and remortgage. If you can't do that, then I imagine your payments will continue for a further 12 months in lieu of that equity.
Buckle your seat belt Dorothy, 'cos Kansas is going bye bye.
I am assuming you have an IVA?? If so there is normally a provision built in that when you get to year 5 you will need to look at remortgaging to release the equity in your home. (does not involve selling) If this cannot be done then you will be possibly looking at a further year added on to your IVA.
Your best bet is to contact your IP and take direct advice from them.