Martin Sambrook, the managing director at Media Audits, said: "Advertisers cannot and will not accept these levels of inflation. They will look for alternatives as they have been for the past 18 months."
The quality of the ITV schedule has been blamed for the decline, but some believe Barb data is also to blame.
"You have to ask what's going on at Barb. Quite frankly, some of the data coming out is still difficult to believe,
one TV sales chief said.
Barb has still failed to install the entire panel and sources have suggested this may not happen until the autumn. The panel has also been criticised for not being correctly weighted towards some audiences.
The chief executive of Barb, Caroline McDevitt, said she was confident of the quality of the data.
"Although the entire panel is not yet recruited the quality of the sample is robust. Anything that people aren't happy about is under constant review,
Although the World Cup is a contributing factor to the increase in revenue, TV sales points are being bullish about the rest of the year.