Tony Shiret caused a stir on Monday with a damning note on Marks & Spencer.

The straight-talking Credit Suisse analyst asked some hard questions about the true extent of M&S’s recovery under Sir Stuart Rose and set out an alternative strategy of his own.

In a 108-page blockbuster, Shiret argued that financial progress has been limited, that M&S is too reliant on older shoppers and should develop a “more relevant, young chain in its smaller stores”, and that Simply Food should be sold.

There are good points well made in Shiret’s detailed note, and it will give investors plenty of food for thought – especially since Rose is expected to stand down in 2011 and there is uncertainty over the succession. No wonder the note prompted M&S’s shares to fall by more than 4 per cent.

The debate about M&S must partly be about fundamentals. When Rose was parachuted in five years ago to fend off bid interest from Sir Philip Green, he pledged to restore M&S’s fortunes based on its original principles of quality, value, service, innovation and trust.

Any retailer that successfully delivered on those values would be a winner, recession or no recession. So the debate then moves on to execution. There’s no doubt that M&S has made some mistakes – loss of direction and position in food, for instance. The traditional values are the right foundation stones for renewed success at M&S, but there’s lots of space for improving execution.

There has been criticism that too much power is concentrated in Rose’s hands since the roles of chief executive and chairman were combined. But, despite the fact that the M&S succession is a frequent topic of conversation in retail circles, there are few obvious contenders.

Assuming he is not pushed out, Rose remains the best hope M&S has. You can bet that he will want to leave garlanded with success and feted as the man who made M&S great again. By delivering on core values – perhaps even by adopting some of Shiret’s ideas – he still can.

Interestingly, despite the travails of financiers, Shiret has been keeping his M&S LBO model up to date. With his many improvement ideas, perhaps the analyst should think about putting together a deal himself.

Or maybe M&S should make Shiret a non-exec director. Whatever else, it would then be impossible to argue nobody on the board dared question the executive chairman.

George MacDonald is deputy editor of Retail Week