Thanks for your question. I will try to help.
You really need to instruct a local solicitor in person to do this for you.
You need a charge drafted by a solicitor which details the money you are proposing to advance him, together with confirming the amount left remaining on any current mortgage he has and the charge would stipulate the amount of money to be repaid and how this is to be calculated.
The charge should also specify that he is under an obligation not to increase the borrowing any further on any mortgage that he current has, so that you can be assured that you would receive sufficient monies to repay the money that you are to loan him.
By instructing the solicitor you can also ensure that they consent of his current mortgage lender is obtained to the charge in your favour which will rank after the mortgage and ensure that it is correctly registered at land registry.
It’s not really something that I could suggest you do on your own as you may put in doubt your ability to claim the money back at a later date if you did it on your own..
It would cost around £350+VAT + disbursements of around £100 or so. Any local property solicitor should be able to do this for you fairly easily.
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