My apologies for the delay - I was called away at short notice
The problem that you face is that since you are not married any claim that you make is made within Property rather than Family law - and Property law is based on purely financial contributions.
In addition there is an assumption that payments that you made were rent for living there
However on the positive side contributions that you made towards the improvement are of the type that increase the value - such as a new bathroom and worktops and doors and under property law that does give you some standing - as does paying the mortgage.
However all this gives you is a possible financial claim on the proceeds of sale - in other words you can force a sale so that he pays you something
You are also entitled to at least two months written notice to leave - maybe three if you need it.
The hard thing to assess is how much you should ask for /are entitled to - given the amount that you have paid and the benefit to the property
probably somewhere between £2000 and £5000 (but you can ask for more!)
The starting point is try try and negotiate with him using Family mediation
Please ask if you need further details