Thanks for your question.
I think you need to speak to a solicitor in your area directly about this.
Basically, you can serve him with a notice to vacate the property referring to the property, your ownership of it, his period of residence there and that you require him to vacate the property by a certain date. You are obliged to give him "reasonable notice" of this, so it depends on how long he has been living there. I would think that 2 months from the date of the notice would be sufficient. It should probably be sent to him at your address by registered post so that you have proof of postage.
If he does not leave after the notice period has expired then you will have to make an application to Court for an order for possession
Because of his financial contribution to the works at the property he may be advised to make a claim on the property under the Trusts of Land and Appointment of Trustees Act. This is quite expensive for him to do. He will not be able to claim half the value of the property though, he would only be able to claim (if he is successful) for the value of his contribution to the works.
So you can see that there are two issues and for this reason I would suggest seeing a property solicitor about writing to him in the hope that the issue as to the works can be resolved informally and at the same time serve him with a notice.
You can find local solicitors using:-
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