Ben and Antonia live together in rented accommodation. Ben also owns a flat which he continues to rent out.
They now decide to buy a new main residence whilst keeping the property which Ben rents out. At the end of the day that is the effective date of the transaction, Ben and Antonia will own two dwellings.
Although they have purchased a new main residence, they will not have disposed of the ownership of their previous main residence (as it was rented) therefore the ADS will apply.