Hi, I am currently living in my partners house and we are separating, I will be moving into another property of his in the next couple of weeks. He has told me that he will allow me to live there rent free and when the property sells he will give me £20,000 for a deposit towards a property of my own. Is there any way of getting this put into a legally binding contract?
Kindest Regards

Consult with a local solicitor that specialises in this type of transaction.
If you don't know of one, ask your local CAB as they will have the right contacts..