The world advertising market is slowing more rapidly than expected, according to data published by media buyer Zenith Optimedia. The figures confirm the gloomy prognosis outlined by many British media companies in recent months.

Zenith's highly regarded Global Advertising Forecasts survey estimates the amount spent on advertising this year will increase by 4.7 per cent - a substantial downward revision of its previous forecast for 2005 of 5.4 per cent.

It says the European market will grow by 3.4 per cent, down from its previous annual forecast of 4.4 per cent and predicts that the US, which drives the global advertising market, will grow by only 3.8 per cent, not 4.3 per cent as previously predicted.

Zenith has also downgraded its forecast for the third major market, Asia. It had previously expected this would increase by 7.1 per cent this year, but it now believes it will grow far less dramatically, by 5.1 per cent.

In global terms, much of the growth will be generated by Latin America, Africa and the Middle East - the only regions where prospects have improved, according to Zenith. It expects Latin America to grow by 5.8 per cent, rather than by the 5 per cent it originally predicted, but the region only accounts for a small proportion of global advertising spending.

Zenith's forecasts provide further evidence of a slowdown in the market, which has performed worse than many observers expected this year. In the UK, major radio groups including Gcap, formed by the merger of GWR and Capital, have reported a falls in revenue. Last week, Daily Mirror owner Trinity Mirror described conditions as 'difficult'.