Andy - you really need to take professional advice.
At least talk to your mortgage company in the first instance, although they will not be independent.
My best advice to you is to get all the information you can, and do nothing for as long as you can.
You need to think about it very carefully - it may be that selling or taking a lodger (tax free on the rent a room scheme) - will be good options for you.
Don't get into arrears in the meantime, tell the council you are single (25% discount in council tax) and don't do anything hasty.
I wish you well.