Sorrell said: "The toothpaste is out of the tube – media agencies have got a taste for independence now."
Media, he said, was arguably more important than creative. Sorrell said: "The main driver for agencies, for WPP, Havas, Omnicom and Publicis, is media, and that has been magnified by the likes of Google and Facebook."
He also said that he believed creative and media agencies were better for having split.
Sorrell was being interviewed on stage at the Ham Yard Hotel by the Newsnight presenter Evan Davis for the final talk in the IPA’s Adapt series, which explores commercial creativity and was started by the body’s outgoing president, Ian Priest.
During the talk, Sorrell remarked that he found the prominent role pitch consultants played in advertising, "remarkable".
"You would think that marketing professionals would know enough to know about where the bodies are buried to run the pitch themselves," he said. "I would never hire management consultants in WPP. Or else, what are we here for?"
Sorrell also flew the flag for networks and said "clients are discovering that fragmentation doesn’t work".
To illustrate his point about the power of networks, Sorrell told a story from his days as the group finance director at Saatchi & Saatchi, when Maurice Saatchi tried to hire Jeremy Bullmore because, despite running a successful creative hotshop, Saatchi craved the respectability that someone like Bullmore, who was chairman at JWT London, could bring.
Sorrell said: "That’s still an important thing. Why does an agency like AKQA get leverage from us? Because we get access [to the biggest clients]."
Sorrell also discussed his succession plan and said that he meets every December with his board to decide who should run the business if he were hit by a truck tomorrow, in two or three years, or in five years’ time.
Prompted by a question from the audience about what he fears most, in relation to his company, Sorrell said that he would have said "Google" a few years ago, but now was more concerned about clients’ focus on costs.
"Clients need to focus on their horizon and not on their boots," he added and warned about the rise of Asian businesses.
Priest will be replaced by Tom Knox, co-founder of DLKW Lowe, as IPA president later this year.
Martin Sorrell is expected to retain his title as the highest paid FTSE 100 chief executive thanks to a £36 million bonus, which could take his total remuneration package for 2014 higher than £40 million.