Luxury brands and retailers have recognised that their most affluent customers are enthusiastically using the internet. In its holiday season quarter, for example, Neiman Marcus, the quintessential US luxury fashion store, reported an 18 per cent increase in online sales from the previous three months to $305m, or 12 per cent of its total revenues.

But new research published today, drawing on a survey of the 12 per cent of American households that account for half of all spending, suggests the wealthy are also using the internet to save themselves tens of thousands of dollars a year.