A rose by any name might smell as sweet but the plan to rewrite Sir Stuart Rose's job title at the head of Marks & Spencer is creating an almighty stink. Just a few months ago Sir Stuart was the toast of the City, the high street - and the Mall. He was knighted in the New Year Honours.Since then M&S's performance has slipped, its share price has sunk, the reputation of its underpants has sagged and Sir Stuart has demanded - and won - a longer and more lucrative contract combining the right to be chairman and chief executive. It was the price of keeping him at the company. City investors are livid.

It is ironic that M&S is drawing fire on corporate governance. Sir Richard Greenbury was chairman and chief executive for most of the 1990s and earned stern criticism for doing so. In 1995 Sir Richard also wrote one of the early reports on corporate governance, though the focus was directors' pay. M&S might have been expected to know better than to incur the wrath of shareholders in the way that it has.

The common practice is for the chairman of a public company to ensure the smooth running of the board while the chief executive takes responsibility for nuts-and-bolts operational matters. Conventional wisdom suggests that a chairmanship is a part-time, partly independent, role.

It is foolish for M&S to act as it has, because it exposes Sir Stuart at an awkward moment. Shareholders are worried that the rejuvenation of the company, which has taken place under Sir Stuart, is running out of steam. Wider economic travails compound the concerns: it has become harder to persuade shoppers to open their purses and wallets. By taking the two top jobs himself, Sir Stuart has no chairman to hide behind. He has ensured that whatever the coming problems at M&S, he is the only man to blame.

M&S has also enraged corporate governance activists who caution that a chief executive working without a non-executive chairman can operate dangerously unchecked. She or he may serve her or his interests, not those of the shareholders who own the company. An executive chairman is also prone to foster a potentially damaging cult of personality at the top of the business. But these fears can be overdone. Only entrenched corporate governance fanatics will now demand the appointment of non-executive chairmen. It is a pedantic mistake to become preoccupied with formulaic separations of particular powers. There are examples that endorse the US model, tolerating and often welcoming powerful individual leaders. Separation, meanwhile, offers no guarantees. The chairman and chief executive of Northern Rock were different people.

The real misdemeanour here is not Sir Stuart's ambition but the board's clumsiness. Lord Burns, the chairman, has not consulted effectively with shareholders and the company has claimed more support for Sir Stuart's new deal than it really enjoys. A more attentive approach would have neutralised ill-feeling. It would help now if M&S gave a fuller explanation of how Sir Stuart and Sir David Michels, deputy chairman and senior non-executive director, will work together.

The most effective, and realistic, next step is for M&S to appoint a chief executive to partner Sir Stuart as executive chairman. Sir Stuart, as Jeremy Paxman might have noted, would be better served by more support in the right places.