The body released figures for the first quarter of 2009, showing revenues for the entire sector were down 19.3% year-on-year to £178.4m.

Digital revenues rose 29% to £16.9m, meaning it now accounts for nearly a tenth (9.5%) of the total.

"It's been going up at a dramatic rate as more networks come on stream," said chief executive Alan James, adding that some previous quarters have seen rises of around 60%.

However, he suggested that the recession may put the brakes on the roll out of some new networks. "In the current climate, it's possible we may not see so many. Those that are planned and put into capex will still go ahead," he said.

James described spend in the first quarter as "volatile" with some expected victors and victims. The entertainment and media sector took the lion's share of the spend at £34.4m and put in a 13.1% increase year on year, while finance, motors and telecomms all fell back.

In terms of advertisers, COI Communications topped the list, followed by McDonalds, BSkyB, Virgin, Coca Cola, Vodafone and T-Mobile.

James said the outlook for the sector was difficult to judge. "While undoubtedly all media are in for difficult times, we believe outdoor will continue to perform well in terms of share as it offers advertisers a wide range of targeted opportunities," he said.