Does my Ex have a right to a share of the property and value increase?

In 1998 my ex purchased a house for 200k on an interest only repayment. 18 months later he lost his business, so to prevent him from having to sell up to a 3rd party, deciding that renting would have been impossible for him to manage whilst living abroad, he had the idea that if I took over his mortgage then he would still have a place to stay when he came back to visit, so we went ahead and his solicitor arranged the paperwork for the sale to myself - at a higher price of 250k so as to look like a normal sale. In truth he hoped to get it back into his name eventually and to this purpose wanted an agreement put in place but we didn’t do this â€Â" I was unsure as both mortgages were interest only loans, and I had paid the full 10 percent deposit of the sale price, & taken on all subsequent mortgage repayments. Effectively on paper it was a sale from him to me.
He came back a few times over the next 10 years, meanwhile marrying abroad and raising children.
I have spent £180,000 on refurbishing the house, paid the mortgage for 15 years. Aside from the first year’s mortgage he has not paid a penny. He has now seen how great the house looks and feels that he deserves a share of money plus 25 per cent of the increase in the house’s value, to the tune of 200k. Does he have a right to this? What if we were still in recession and I was in negative equity â€Â" would he still be asking and could I have had a right to ask him to pay half of all the monies I have spent on the house?

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