Is that all he has done
. In 3 years!!! The painting of the rooms and flooring I would consider normal living in a house and not important with regards to house value. I do them myself here 
The loft, well if he has only half done it, sent you that abusive text (please say you have kept it) saying fuck off and pay someone else to do the rest of the work. Then well not really added much there as you would need to pay someone to complete it to a usable standard (that could all be deducted from his 'share' of the value).
My bathroom was done in less than a month, cost around £5k in total including all parts & labour. Is it an additional bathroom or the original one replaced? An additional one may have added value but his contribution was at max a couple of £k labour.
Not had my boiler replaced however my central heating pump went bang about a month ago and all in parts and labour cost me £1k to get it back up and running.
No idea about a drive however again I would imagine a £k or 2 in labour max.
So while you could agree that the work he has done has helped increase the value of the property his contribution to that increase is what £5k max in labour???
Is all his work certified and signed off? Especially the boiler etc? If not get it checked for piece of mind and any estimates for corrections that need to be done can again be taken from his 'contribution'.
How much did his car cost? How much did his van cost? How much reasonably would you argue your work for his business is worth and how much did you put into that business. Bet that is going to be far more than his £5k contribution.
He has not paid towards the mortgage, council tax, food, bills, heating, water (you can named the rest) apart from the last few months (when he was planning on leaving you and setting up his escape plan).
I think any reasonable lawyer could make mince meat of this guy in 2 letters flat.
Not done it all. I just know that from reading on here most women are advised to register a claim somehow via the land registry if they leave a long term relationship and think they have a right to the share of the property. So if you start there you will know where you stand right now.
That could change of course if he does try to register a claim. Do you think he is that smart?
I think it pays you to carry on being seen as nice and reasonable towards him for now while you get all your cards in order then if he does try this I think (if you stop being so nice) you will blow him away in small order.