I looked into the One Account some years back � when I think it was originally run by Virgin.
The general consensus of the financial press was that they are not all they are cracked up to be.
However if you are the type of person who typically has �1,000 - �2,000 sitting in you current account, then they could be for you. My understanding of the way they work is that let�s say you have a 25 year repayment mortgage of �100,000 � you will pay the set monthly mortgage payments. However your outstanding mortgage of �100,000 (or whatever) will be reduced by the amount in your saving account (say �,2000), so you will effectively be overpaying the mortgage � which results in it being paid off sooner.
You need to take a close look at the average amount in your current account, over a typical month. If like me, your salary is paid into your account at the start of each month � and almost immediately is paid the mortgage, council tax, credit cards, standing order utilities etc � leaving a small amount for you to survive the rest of the month � then these accounts are not for you.