A British advertising company is proudly claiming to have built the world's largest database of individuals' internet behaviour.

WPP claims it will track "almost 100 per cent" of the UK population. It is run by the British businessman Sir Martin Sorrell.

Many of these outfits are pooling customer data into WPP's new database venture, called Xaxis. Brian Lesser, chief executive of Xaxis said that it cant do all that because the internet is an advertising-supported medium.

Much of the web is free because advertisers want to put messages in front of people and Xaxis is  supporting the broader internet economy by improving the targeting of ads, he told the Independent.

It has built individual profiles of 500 million internet users across the world, covering, it says, almost 100 per cent of the people online in the countries in which it operates, including the UK, US, Australia and eight others.

WPP insisted the information had been "anonymised" but as the Electronic Frontier Foundation has pointed out knowing the pattern of websites you go to makes it easy to identify individuals.