Marks & Spencer's chief executive, Roger Holmes, faces being forced out by shareholders if trading does not improve in the coming months.
After last week's dreadful sales figures, the focus is on the review by Vittorio Radice, the head of homewares recently given responsibility for clothing.
It is thought he will present his findings in time for the full-year results at the end of May, and shareholders say this will be a critical time for M&S.
One investor said he wanted to see signs of stabilisation by the May update and over the summer. Commenting on Mr Holmes' tenure he added: "The board won't be doing its job if it doesn't see any sign of improvement in the next six to nine months and doesn't take affirmative action."
Another institutional investor said the pressure was now "piling on" Mr Holmes, who took over from Luc Vandevelde in 2002. The investor recently sold out of M&S, concerned by the retailer's weak trading. But he said he would consider buying back if Mr Holmes were replaced.
M&S's new Lifestore outlets have also caused concern. "It is spreading itself too thinly," the former investor said.
M&S may now become a bid target. One shareholder said: "M&S looks more vulnerable to a takeover than Sainsbury's. There is more speculative buying of Sainsbury's shares, but on the numbers I have done, M&S is now more likely."
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