Hello and thanks for your question.
When a lender agrees to lend the money for a mortgage, because it is a large sum, the lender is looking to reduce the risk to them as much as possible.
One way they reduce the risk is to have more than one person named on the mortgage. When two people are named on the mortgage deed, it means that they are bioth joitnly and severally liable for the mortgage debt, and if the mortgage goes into arrears, the lender can chase either one of them for the WHOLE of the mortgage debt.
Second way is to ensure that the combined income of all those named on the mortgage deed is at least equal to one third (or soem lenders will allow one quarter) of the total mortgage debt.
Your partner will therefore have to have a large income to be able to persuade the lender to put the mortgage in his sole name.
The lender cannot be made to agree to this.
The other way that the lender reduces their risk is by securing the mortgage against the property. All mortgages include clauses which state that if the mortgage gets badly into arrears, they can repossess the property (by getting a court order).
The lender is not going to want you as a joint owner causing difficulties in court proceedings if they apply for a possession in respect to a debt in the sole name of only one of the owners, so I think they would not be happy that the mortgage remains in joint names while the mortgage goes into one person's name.
I am not say that this would be illegal - but I am saying that I don't think any lender would agree to transfer the mortgage into your partner's sole name while your name remained on the title deeds jointly with his.
I also think that you should both take independent legal advice - I suspect that any solicitor would advise your partner that it makes no sense for him to bear all the risk by taking on sole responsibility for the mortgage, while you continue to share in the benefit of any increase in value of the property as time goes on.
I hope this helps and I wish you the best of luck.
Thanks and best wishes...