Declines in global advertising will be much worse than expected, says a leading media buyer , which will on Tuesday unveil the grimmest forecasts yet seen for the advertising market and traditional media companies.

Worldwide advertising spending, a barometer for economic confidence, will fall 6.9 per cent in 2009 to $453bn, compared with 1 per cent growth last year, predicts ZenithOptimedia, the media buying unit of Publicis, the world’s fourth-largest advertising group.