Mortgages and Deeds

[MrsPotts17]

During the divorce process a few years ago, DH offered to sign over his former home he shared with his ex to ensure their son had a nice home in a nice area to grow up in.
The judge agreed that she may have the house and contents but that she must remove DH from the mortgage, all associated bills and financial matters. It was clear on her bank statements she showed to the court that something was not right. She had transferred in excess of 20 grand to her mother as a "gift" and made out she was jobless and on benefits. In reality she worked as a NHS nurse at the time and still does in the same clinic she has worked in for 10 years.

DH agreed for her to change the direct debit for the mortgage into her personal account. She then took him off the deeds but then left him on the mortgage. She said the bank wouldn't let her take his name off because of affordibility. DH rang the bank and said that she had not contacted them at all but informed him that it must be a joint application to remove one party from the mortgage. Ex refused and told him to get lost. Many years later he is still on the mortgage (not paying it) but not on the deeds. Ex has paid it every month without fail with no delays so it is clear she can afford it. We even asked the bank to offer her a remortgage over a shorter term, significantly cheaper each month and in her name alone. They did and she laughed and said there is no way she is removing him in case he ever wants to buy a new home then being on her mortgage could possibly stop him from being happy in a new home.

My question is - can he then go back on the deeds and have rights to this house again if he is still on the mortgage for the next 15 years at least. Or does he have to go to court? But does he take her or the bank to court?