Privacy campaigners reacted with concern when earlier this week the competition watchdog said banks should share customers' data to help them find the best deal.

Those campaigners have long missed the boat.

Our financial data is already so widely shared, stored and available for inspection by a range of private and public bodies that the genie is well and truly out of the bottle.

Take credit reference agencies.

Most consumers think that credit reference agencies simply collate data about our repayment of loans. But these vast and rapidly-growing businesses go far further than that. They are now cashing in on a new area of personal financial data: the capturing, and selling-on of details about our income.

Down to the last penny, in millions of cases.

In fact Equifax, one of the big three credit reference agencies, even boasts (to business customers) that it collects information for such tiny transactions as one consumer repaying another "for an evening out".