The backstory:
My parents divorced some 20 odd years ago, after the divorce was finalised they got back together but never re-married, in the past they always bought their homes in joint names but when they bought their last property my mum had a bad credit score and their lenders wouldn't let her have a mortgage, so my dad got the mortgage in his name only. Only his name went on the deeds for the property.
Nearly 4 years ago my mum and dad finally went their seperate ways, it wasn't pretty due to my mum being very toxic, at the time she visited the Citizens advice bureau and was told that since she had no dependants (both children left home with families of our own) and her name wasn't on the property deeds she had no legal claim on any of the equity on the property. Despite this she told me that she'd registered a claim on my dad's house through the land registry??? I didn't take much notice because it just didn't seem right.
My dad knew he didn't owe her any money in the legal sense but morally felt it was right to give her a decent pay off, so he said she could have whatever she wanted from their home (furniture, electricals etc), and also valued their home and gave her half of the equity to enable her to set up a new life elsewhere.
My dad stayed in the house for a while but has now remarried and lives with his new wife. He rented his own house out for a while but is now trying to sell it. He has a buyer now and the land registry searches have shown that my mum has registered a claim on the property, and it can't be sold until she lifts it. My parents are not on good terms, he's asked her to lift the block but she's refused and is now demanding more money to lift it. My dad's solicitors say they can't proceed with the sale until my mum does this but that's not going to happen.
On the other hand, in the last few years the property has lost £30k in equity so technically she came out of it with quite a lot more cash than my dad will. He has bank statements to prove she took her settlement so what can he do now?
Any ideas?