You will need to be shown as a joint registered owner of the property is you wish also to be put on the mortgage. You will need to involve a solicitor for this for a Transfer of Equity. The Transfer itself does not need to be for any monetary value but the solicitor will need to ask the mortgage lender whether they have any objection to you becoming joint owner and mortgagor. The solicitor will have to have a bankruptcy search against your name to make sure there are no pending orders against you. If the lender has no objections you will also need to sign a new mortgage deed. You should take legal advice as you will be jointly and severally responsible for any mortgage debt over the property meaning that if, hypothetically, if your partner moved out and was untraceable, the whole mortgage debt will fall on you to pay.