Luc Vandevelde, hailed as the saviour of M&S, is ousted by the board

For a fiftysomething Belgian accountant with a lifetime's experience of managing European food brands, he made an unlikely pin-up for the British consumer. But when Luc Vandevelde turned round the fortunes of Marks & Spencer within two years of taking over, he became the most celebrated of his countrymen this side of the North Sea since Plastic Bertrand.

Today the company announced that "Cool Hand Luc", as he was called by an admiring British media, is stepping down as M&S chairman because of "personal commitments" to the family of Paul Louis Halley, one of the major shareholders in the French hypermarket operator Carrefour. Mr Vandevelde joined the board of Carrefour after Mr Halley was killed in a plane crash in December.

"A search is under way for a new chairman and Luc will remain in post for as long as necessary to establish his successor," M&S said.

The announcement came after concern that he has been exerting too little of his considerable energy on the nationally revered retailing giant, and that the miracle he is credited with performing is nothing more than a mirage.

M&S shares slumped last month to their lowest level in a year as it was revealed that sales of clothing, general merchandise and homewares had fallen 5.2 per cent between January and March. Sales of food - which in recent years have cancelled out a weak performance in clothes - were also down, blamed on the retailer's failure to wake up in time to the low-carb diet revolution.

Negative headlines surrounding its latest range of teenage clothes - complete with an 11in micro skirt, fishnets and boob tube - revealed the torment facing M&S executives as they try to reposition it as a credible youth brand.

More worryingly, sales of homeware ranges were also down 13 per cent - despite the opening of its much-vaunted Lifestore in Gateshead.

Mr Vandevelde's critics seized on his growing commitments to businesses other than M&S to demand that he step down to allow the company to concentrate on redefining itself for the modern world and to undergo the cultural revolution it so desperately needs. In addition to his role at M&S and on the board of Carrefour, he is a non-executive director of the mobile phone giant Vodafone and is executive chairman of Change Capital Partners, a private equity fund that targets retail companies across Western Europe and which has prompted claims of a conflict of interest with his role at M&S.

City headhunters have already been charged with finding his replacement, according to weekend reports. Among the names being touted to succeed him is a former Tory party chairman and Asda chief executive, Archie Norman.

Mr Vandevelde had reportedly agreed that he can no longer devote enough time to the business. One member of the M&S board was quoted as saying: "He read the board's mood precisely. We were fed up with how little time he was spending here, so we were close to asking him to leave."

Pressure is on to find a new chairman before the company's annual general meeting on 14 July, when Mr Vandevelde would normally be expected to issue a rallying cry to investors.

Sue Sadler, M&S's corporate press manager, said yesterday of suggestions that Mr Vandevelde was falling short in his duties: "Luc is a part-time chairman and is spending the right amount of time for the job."

When he became part-time executive chairman last September, it was widely reported that he should spend 60 per cent of his time with the retailer.

He is said to have earned more than £8m in his four years at M&S. As well as a permanent hotel suite at Claridge's, widely thought to be paid for by the company, he enjoys a basic salary of about £420,000, now paid entirely in M&S shares. He also collects a total of £100,000 for his work at Vodafone and Carrefour and an undisclosed figure for the two days a week he puts in at Change Capital.

Robert Talbut, the chief investment officer of Isis Asset Management and the first person publicly to question the chairman's commitment to M&S, said yesterday that investors would be relieved at the announcement that Mr Vandevelde was standing down. "We welcome the clarification of Luc's position, and our position is that M&S in its continuous process of transformation requires the majority of the time of a fully involved chairman," he said.

But M&S observers say there is still a long way to go, and the problems it faces are still many and varied. And while Mr Vandevelde initially gave the company a boost - putting in train the much-needed process of change - he has been overwhelmed by the scale of the task.

HIS OTHER DIRECTORSHIPS

VODAFONE

Luc Vandevelde was appointed an £85,000-a-year non-executive director in July 2003, prompting speculation that he could succeed Lord MacLaurin of Knebworth as its chairman eventually.

CHANGE CAPITAL

He is managing director of the private equity fund. He works two days a week from its Chelsea headquarters seeking medium-sized Western European companies valued at between €30m and €500m.

CARREFOUR

He returned to the board of French supermarket chain Carrefour - Europe's largest food retailer - in March. Mr Vandevelde served as vice-chairman during its merger with Promodes in 1999 before leaving to join M&S in 2000.