Speaking to Media Week, McCulloch added: "Advertisers have been gifted CRR and they have exploited it, but we're now reaching the point where the model is unsustainable."
ITV is warning advertisers that a crisis is looming over the only commercial channel able to challenge the BBC for major audiences on a regular basis, and that it could be forced to make cut-backs to its programming budget as early as next year.
Allowing for an overall decline of 5% in the TV ad market, ITV1 stands to lose approaching 拢250m in advertising revenue next year.
"The revenue situation in the market has thrown it into stark relief. It's no longer an issue for a few years down the line. This is a right-now issue," said McCulloch.
Last week, Media Week reported how the biggest spending TV advertiser, Procter & Gamble, had called for a timetable to end CRR, with Bernard Balderston, associate director for UK & Irish media, saying he feared advertisers would live to regret the damage being done to ITV1.
However, this issue looks like causing major divisions, with the Incorporated Society of British Advertisers saying the majority of its members want the CRR to remain in place.
Ilker Shakir, investment director for Unilever at MindShare, said he believed CRR should remain in place, adding that the same principles were behind the decision to slash the value of its separately negotiated, four-year advertising deal across ITV.