The Office of the Adjudicator is responsible for ensuring ITV adheres to the terms of the CRR mechanism, which allows advertisers to pull spend from ITV1 proportionate to any declines in its audience share.
Under CRR, ITV is not allowed to connect the sale of its digital properties to ITV1. However, some agencies believe ITV is selling its digital channels in conjunction with ITV1.
One agency's head of broadcast said: "ITV is aggressively selling ITV digital and trying to force agencies to put back any money that comes out of ITV1 back into ITV digital. It isn't meant to conditionally sell, but wants to gain a whole extra percentage point [of TV ad spend] this year and is leveraging its assets as much as possible. If it continues like this, I wouldn't be surprised if agencies go to the adjudicator and make a complaint in confidence."
ITV declined to comment.
Meanwhile, with only weeks to go before the end of the TV trading season, Five is thought to be facing tough talks with agencies, coming under fire for a lack of definitive content.
Another agency's head of broadcast said: "The problem with Five is that it's the easiest to drop off your schedule and, from my experience, clients aren't that upset if they don't appear on it because the offering isn't that unique. You have to pull spend from somewhere.
"Last year, Five had its digital portfolio and Neighbours to talk about. This year there is very little."