Broadcasters indicated total TV ad revenues, which were down by 2 per cent in both January and February, could slide by at least a similar amount during March. One sales director predicted a "double-digit" drop in March, but rivals dismissed this as "exaggerated".
Even a fall of 2 per cent across the first quarter could see close to £20 million of revenues coming out of the TV market.
ITV's share price has suffered recently, partly owing to uncertainty over levels of ad spend this year as consumer confidence slides.
One media agency source said: "If March isn't good with Easter falling in it, then that doesn't bode well for the rest of the year."
The decline in TV revenues has hit TV companies despite 2007 being a good year for commercial television.
Barb figures, which have been released this week, show commercial impacts rose by 3.9 per cent during 2007, including a 1.5 per cent rise among 16- to 24-year-olds.
Tess Alps, the chief executive of Thinkbox, said: "People are watching more TV than ever. This is historic news for advertisers."