By Jeff Randall BBC business editor

Stuart Rose will be keeping a close eye on M&S's share price

When he says (as they all do) he is going to deliver shareholder value, the stock market now knows exactly on what basis to judge his achievements.

Not for Mr Rose the luxury of amorphous "internal targets", confusing comparisons with corporate "peer groups" or other dubious yardsticks by which underperforming captains of industry like to be assessed.

No, for the new M&S boss, the minimum requirement is an M&S share price of 370p.

That is the number that will be sewn into the lining of Mr Rose's immaculately cut suit: because that is the price that Philip Green, the retail tycoon, is prepared to pay in cash for M&S's shares (it values the company at nearly �8.5bn).

Given that before Mr Green turned up, M&S's three-month average share price was 280p, you might be forgiven for thinking that a bid of 370p in real money (not hard-to-value stub equity) deserved serious consideration. But M&S's directors didn't see it that way.

Impatience

In a note to clients, Deutsche Bank's retail analyst said: "We believe that M&S should at least have consulted shareholders before it rejected the proposal (from Mr Green)."

Will Philip Green have to keep his cash?

But so sure is the M&S board that the company is worth much more than Mr Green is offering, it took the directors less than two hours to dismiss his proposal as "seriously undervaluing the business".

In doing so, they have in effect turned to Mr Rose and said: "We've got rid of Mr Nuisance. Now it's up to you. Show us that you can do better."

Of course Mr Rose will not be expected to produce a soaraway share price overnight. He will be given some time - but not as much as he would like.

In the eyes of the City, time costs money and the big professional investors are famously impatient.

It's not uncommon for incoming chief executives to tell shareholders of troubled companies that a turnaround will take three years. Mr Rose has nothing like that - and he knows it.

Supermarket squeeze

At best, he has 12 months to prove to the company's supporters that through a combination of better buying, improved housekeeping and old-fashioned hard graft he can restore one of Britain's iconic brands to its former pre-eminence.

M&S has been squeezed by competitors and the supermarkets

On 12 July he will unveil his operational master plan for making M&S a more modern and efficient business. Some serious cost-cutting seems inevitable, including a streamlined management team, fewer consultants and other backroom job losses.

In fairness to Mr Rose, the task of running M&S has become considerably tougher in recent years. Shoppers are more demanding, competition from other fashion groups is stiffer and the supermarkets are hacking away at M&S's clothing and food sales.

So much for Mr Rose, but what about the maverick Mr Green?

Had he launched a 370p-a-share cash offer a month ago, when M&S was led by the hapless Roger Holmes, old ladies and small children would have been knocked over in the rush to grab the readies.

But Mr Rose has given investors a reason to believe; an excuse for sitting tight rather than cutting and running.

Time will tell

It's not that shareholders were itching to hand over the keys to M&S. Indeed, many suspected that if they sold to Mr Green, who has built his reputation on acquiring under priced assets, they would be giving away imbedded value.

The problem, however, was that they didn't fancy Mr Holmes's chances of unlocking that value. Clearly, Mr Rose is regarded as a very different proposition.

Having been shown the door by M&S's directors, Mr Green's only hope of success now is to appeal directly to the company's shareholders. It's a long shot. Though it's not unprecedented for investors to ignore the recommendation of the board, it is unusual.

Thus the most likely outcome is that Mr Green will withdraw, while Mr Rose pedals the bike ever faster to reward the enormous faith that M&S loyalists have put in him.

Philip Green will keep his cash; Mr Rose will have the aggravation. And in a year's time, we'll all know who was right and who was wrong.