This is the more modern approach to mortgages, designed to fit into a modern lifestyle. It combines a mortgage and a standard current account, they are ideal if you want to make overpayments, or receive irregular bonuses. The other main advantage is that the interest is calculated on a daily bases, therefore, when you pay money into the account it reduced the overall loan size, thus reducing the overall loan size paid.
Think of this method as a current account with a very large overdraft. Your salary gets paid every month, reducing your overdraft therefore reducing your interest. Even when you make withdrawals from your account the total overdraft has still be lowers, this the interest.