Marks & Spencer was facing a full-scale investor revolt last night after Schroders, one of its top ten shareholders, made a devastating attack on the retailer's plans to give the chief executive, Sir Stuart Rose, the additional role of chairman.

Richard Buxton, the head of UK equities at Schroders, said that M&S was setting an “appalling example” and cast doubt on its claims that it had widespread investor support for the boardroom shake-up.

“We don't believe there's been any consultation and we've not been able to find any shareholder who's genuinely supportive of it,” he told The Times.

Mr Buxton, one of the most respected equity fund managers in the City, said that Lord Burns, the chairman of M&S, had given him the “brush-off” when asked for an explanation. He also said that he doubted M&S's argument that Sir David Michels, the deputy chairman, would provide a counter-balance to Sir Stuart.

The intervention by Schroders, which owns a 2 per cent M&S stake worth £130 million, leaves in tatters the retailer's claim that Legal & General, which owns 5 per cent of M&S and has already criticised the boardroom changes, was a solitary voice in opposition. The Association of British Insurers too has expressed reservations and demanded an explanation of the boardroom changes.

Mr Buxton said that the planned promotion of Sir Stuart to executive chairman went against ten years of corporate governance best practice.

“For such a household name, it sets an appalling example,” he said. “We're dead against. First and foremost, it's an undue concentration of power. It means there isn't going to be any realistic questioning of the strategy set by Sir Stuart at a time when the trading over Christmas demonstrated there might be some serious questions to be asked.”

Mr Buxton hinted that M&S ought to rethink even if it meant losing Sir Stuart completely. “The company is bigger than any individual,” he said.

Sir Stuart had made plain to Lord Burns he would not stay at M&S unless he was given the additional powers.

Mr Buxton, who runs the £1.5 billion Schroder Alpha Plus fund, also criticised M&S for its handling of Schroders' concerns. “We wrote to Lord Burns stating our objections. We received a brush-off reply from the company secretary saying they would be writing to all shareholders shortly.”

M&S has already come under fire for its lack of consultation over the controversial move. L&G was given an hour's notice before M&S went public on March 10. M&S only gave advance notice at all to four or five shareholders.

Although Sir Stuart is deemed to have done a good job at M&S over the past three years, doubts have crept in over his strategy because of the recent shrinking of underlying sales. The shares have plunged from a high of 750p a year ago to about 400p.

M&S last night declined to comment. It has argued that the elevation of Sir David and the appointment of an additional non-executive director would provide a counterweight to Sir Stuart.

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