Sorrell left the business in April following an investigation into an undisclosed allegation of personal misconduct.

Speaking at an event held by The Drum during Cannes Lions advertising festival, Sorrell claimed his departure was badly handled by WPP.

He said: "There are other courses of action that were open to the company, which they did not take."

He suggested he had been undermined by a WPP source leaking information to the Wall Street Journal. "The most damaging thing that happened during the course of those events was the leak over the Easter weekend at the very top of the company and to which there has been no investigation whatsoever."

Sorrell also dismissed media reports on the reasons for his exit, including rumours that he paid for a sex worker using company expenses, as "fanciful".  

Addressing suggestions that he was a bully towards staff, reported in a Financial Times exposé, he said: "Am I the easiest person in the world to get along with? You know that I am difficult, but if it’s a fault to demand or expect excellence then mea culpa."

He also discussed his new venture as chief executive of shell company S4 Capital, which is backed by £40m of his own money. He said: "The structure of S4 Capital will be very different in structure than anything we saw at WPP."