Karl - noted and appreciated but there's only clarity when a lender actually discharges their legal charge formally.
I would suggest trying to identify the account number through any old paperwork/account info your Mother may have access to
You can also use our contact form to submit specific details re the address/title number and what details you are trying to confirm. The support team can then check to see what information, inc any account number if provided, exists in our own archives
Public guidance: dealing with land and property - GOV.UK