Online advertising is racing ahead in Britain, growing at roughly 40 percent a year, and is expected to account for as much as 14 percent of overall ad spending there this year, according to WPP Group's Group M.

That's the highest level in the world - and more than double the share for online advertising in the United States, according to media buying agencies, as reported by New York Times. Britain lagged behind America in the proportion of online ad spending just four years ago. But in 2003 it overtook the United States, and this year the internet will account for 10.5 percent of British ad spending, compared with 5.6 percent in the United States, according to IAB estimates.

The shift can be attributed to Britain's explosive surge in broadband access, more experimental media buying, and American media buyers' lack of trust in web metrics and their love of TV spending.

TV advertising has held strong in the United States, where about $72.56 billion will be spent on TV ads this year, according to Interpublic Group's Universal McCann. That constitutes a quarter of all ad spending, and that proportion has held roughly steady since 2000.