Marshall Manson – who leads Brunswick’s digital offer in the UK, Europe and elsewhere – said there was "zero" relationship between success at Cannes and commercial success, and Cannes had become "a parody of itself".
The former UK CEO of Ogilvy PR made the comments at the PRCA/PRWeek Roundtable on Digital Creativity on Tuesday.
Manson, who stressed that he was expressing a personal opinion, pointed to a typical situation whereby agencies would decide at the start of the year to look at what work can be done before the entry deadline, solely to win a Lion.
"I think Cannes awards are BS, I really do," he said.
"Too many of the entries for Cannes are contrived just to be award entries. Nonsense stuff that no real human being ever saw. Claimed results that are cooked. Campaigns with no budget behind them. Posters that ran once or twice, just enough to satisfy entry requirements. Recognising this sort of work makes the whole thing a fraud, and that’s a shame, because recognising good creative work is important."
The Brunswick partner said he was "not blaming the judges", who are "generally conscientious". "But they have to take the entries at face value, and too many of the submissions are just bogus.
"I think the idea of a festival of creativity is great, and genuinely important. But Cannes has become a parody of itself. Too many silly awards. Too much winking and nodding. Its credibility is eroding fast.
"There is zero relationship between success at Cannes and commercial success. None."
But Simon Cook, managing director of Cannes Lions, explained that submitted work was subjected to intense scrutiny before it was put before the jury.
He said: "Each piece of work that is entered into the Lions is reviewed several times before it's even put in front of a jury. We apply different lenses to ensure it meets our criteria and if necessary we'll contact the company who entered or the client who commissioned the work, in order to verify it if needs be. Cannes Lions appoint a world-class jury of experts to make the correct call."
Cook said there was also evidence that winning entries positively affected a company's success.
He added: "There is a wealth of evidence out there that proves that Lions-winning creative work is linked to commercial success. Take the Case for Creativity research, which found that the majority of former recipients of the Creative Marketer of the Year award – companies like Burger King, Heineken, Samsung and Coca Cola, all of whom have won multiple awards in Cannes - happened to experience an all-time share price high at the time of receiving this accolade."