The news will come as a blow because earlier advertising forecasts had shown that the market had begun to pick up over the summer.
The figures show that ITV is losing market share as rivals such as BSkyB and Channel 5 gain.
ITV's cumulative advertising total for the first nine months of this year has fallen 2.9% on last year.
ITV is also suffering from lagging TV audience figures. In July, it is believed to have recorded its worst viewing figures in its history.
Figures from the British Audience Research Board published in the Sunday Telegraph show that ITV attracted 22.4% of the TV audience, down from 24% in June. In July 2001, the broadcaster had an audience share of 27.1%.
ITV attributed its poor performance to the summer being a particularly weak period for audience figures, compounded by competition from the BBC's coverage of the Commonwealth Games and Channel 4's reality TV show 'Big Brother'.
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