The answer here depends on whether you are a married/in a civil partnership or are unmarried. A husband and wife each own a residential property (with neither having any interest in the other’s property) but both live in the property owned by, say, the husband, with the property owned by the wife being rented out. If they sell their main residence and jointly buy a new one the higher rates will not apply to the joint purchase. As they are married and have both lived in the property owned by the husband as their main residence they will both be treated as replacing their main residence, even though the wife retains the rental property. An unmarried couple (A and B) each own a residential property and both live in the property owned by A, with B’s property being rented out. If the main residence is sold and they jointly purchase a new one, which will be their new main residence, the higher rates will apply to the joint purchase of a new main residence. As they are not married (or in a civil partnership) B will not be treated as replacing his main residence as, even though he has been living in the property owned by A, he has no interest in the property A is selling.
