Marks & Spencer was on the rack today after a top City analyst raised serious doubts about the future of the High Street giant.

Tony Shiret, a long-standing critic of the company under the leadership of Sir Stuart Rose, issued a 100-page research note of unusual brutality, entitled Do The Right Thing.

This appears to be a hint that Rose should quit his role as executive chairman and effectively admit that his five-year tenure has been a failure. M&S last year unveiled profits of £1 billion for the first time in a decade, but the City was already sceptical about whether a true turnaround had been achieved.

Sliding sales and a large profit warning duly followed. Shiret, the retail analyst at Credit Suisse, today set a price target for the shares of just 160p as he predicted profits this year will be £560 million, falling to £328 million in 2010. At that level the dividend would be hard to sustain.

He argued that M&S has made very little progress under Rose, with cost savings driving a balance-sheet improvement that was temporary, and little sign that deeper structural problems have been addressed.

"The current regime has not delivered on strategy or stability, and shows no sign of doing so," he said.

"If the pattern of profit-forecast reduction continues for much longer, we would expect it to be very difficult for the current management to remain."

Rose was promoted to executive chairman from chief executive last year, a controversial move that some said gave him too much power.

He has also been criticised for failing to have an obvious successor in place.

Shiret argues that Sir Stuart has not revitalised the brand, relying on older customers of 55 and above who are not being replaced by younger shoppers.

The analyst thinks the City is under-estimating just how big M&S's problems are, and that matters will come to a head before long.

M&S had no comment on Shiret's remarks. The shares today fell 11p to 250p.

Rival analyst Nick Bubb of Pali International said in a note to clients today that the entire clothing sector is "bedevilled by overcapacity".

Supermarkets such as Sainsbury's, Asda and Tesco have lifted clothing sales of late, a further blow to M&S and others.