What is my partner entitled to if we part company?

My partner has been contributing to the mortgage for around six years. The mortgage is in my name as I purchased the house from the council. I have lived in the house 25 years and my partner had his own property when I met him. He was not entitled to be on the mortgage as he had not resided in my home long enough. He has now got himself into a situation where he owes a substantial amount of money to someone.

This has put myself and my family into a vulnerable place and I am now trying to get advice as to what he would be entitled to if we part (I think this will be inevitable). I need to be prepared for the future and do not want find myself in a position where I lose everything due to another persons stupidity.

Could you please advise?