Post Graduate Student Mortgage

Hi,

My daughter (a post graduate student) would like to buy the flat she is currently renting from her older sister.

Her older sister wants to sell the flat, so is looking to do a deal that will suit both of them.

It is a two bedroom flat, with the second bedroom rented out on a causal basis. (no contract)

If she draws up a contract for renting out the second bedroom, will that count as income when applying for a mortgage? She does have other income as a lecturer at the Uni, but not enough to buy the flat.

Thanks,
Pete