Rent division

Mr A and Miss B have been living together as a couple for several years but remain unmarried. They live together in a property owned by Mr A and since she moved in with him Miss B’s former private residence is now rented out.

The couple have recently purchased another property in their joint names and also intend to rent this out. Their long-term plan seems to be to build up a property portfolio to supplement their pension income in retirement.

Mr A is in full-time employment and pays tax at the higher rate of 50% while Miss B is a basic-rate taxpayer who works on a part-time basis. She has time to administer the lettings and deal with any problems that arise.

My question is even though this property (and presumably any future ones) is held in joint names...