Residential Letting / Rent a Room Scheme

[sammd]

If you decide to opt out of the Rent a Room Scheme and pay tax on 'net profit' instead, one of the 'allowable expenses' is 'interest on property loans'. Does this mean interest on mortgages or other types of loans?

If you own the house jointly with someone else, but only you are living in it, is it assumed you're letting it by yourself or jointly?

Thanks for any help.