IT is one of the clichés of big business that companies are run, not by the chief executive, but by a team of senior managers. The City, of course, takes not the blindest bit of notice, and nor does the media.

Think of Sir Terry Leahy and Tesco, or of Stuart Rose and Marks & Spencer, or of Philip Green and British Home Stores. The personal identification is almost total, in these and many other cases.

But to every rule there is an exception — and last week he announced he was leaving BT Group. Pierre Danon runs only about a third of the phone group, but in his four-and-a-half years there he has cultivated a much higher profile than his boss, Ben Verwaayen.

There are legitimate reasons for this. As chief executive of BT Retail, Danon was responsible for supplying millions of residential and business customers, constantly under attack from low-cost rivals and the appeal of mobile phones. Quick and decisive, Danon personally led BT’s spirited defence with a blizzard of initiatives — new and simpler pricing tariffs, the rollout of broadband internet, BT’s return to the mobile market, and many more.

But this was not the only explanation for Danon’s outsize reputation. The Frenchman’s ambition shone through in everything he did. Few believed him when he said he had not been interested in becoming group chief executive instead of Verwaayen. His own staff fell about laughing when he told an interviewer: “I have absolutely no ego.”

Danon’s departure, to become chief operating officer of Cap Gemini, the troubled IT services group, immediately became the subject of telecoms industry fascination — coming as it did only weeks after a widely reported, and emphatically denied, boardroom split.

People who know him struggled to understand why he was moving, if not to become chief executive of a big company. Cap Gemini is based in Paris, and Danon has repeatedly said he much prefers the world of British business.

Jean-Yves Charlier, who was a senior manager at BT before his recent appointment as chief executive of Colt Telecom, said: “Pierre has a very big ego and a very big career aspiration. His aspirations are much more to look to the chief executive role. It’s a great loss to BT.”

Such was the certainty in the scale of Danon’s ambitions that his new boss, Paul Hermelin, offered assurance that he was not about to be replaced. “My succession is not open,” he said. “Today I remain in charge.”

BT, meanwhile, poured praise on Danon. Verwaayen said Danon had done “a superb job”. Sir Christopher Bland, BT’s chairman, chipped in with thanks for his “tremendous contribution” to transforming BT.

Cynics thought that BT was trying too hard to quash suggestions that Danon had fallen out with Bland and Verwaayen, and that explained the timing of his departure.

One BT insider said: “He’s a supreme strategist. He does not do anything without having thought it through. Even when he appears to make off-the-cuff remarks, he’s thought about it. He’s a trained lawyer and engineer. Nothing is left to chance.”

One theory is that Bland has decided to renew Verwaayen’s contract, thus scuppering Danon’s hopes of advancement. It has been rumoured that Verwaayen was interested in returning to his native Netherlands, to take up a political role.