The apparent failure this week of a bid by former Rover Cars manager, Mr John Towers, to buy the company from BMW has rekindled British resentment against the Bavarian car firm and its chief shareholders, the reclusive family of Ms Johanna Quandt. The row over Rover Cars will probably blow over soon after BMW finalises its sale to the venture capital firm, Alchemy.

But the disastrous mismanagement of Rover has raised questions about the future of BMW as an independent company and fuelled speculation that the Quandts are preparing to sell their 49 per cent stake in the Bavarian carmaker.

"The sale of BMW suits the wishful thinking of some competitors. But it has no real basis," the Quandt family's spokesman, Mr Thomas Gauly, said last week.

The motor industry has certainly been good to the Quandts and the family's stake in BMW is now worth 10 times what it was in 1982 when Johanna's husband Herbert died. Herbert was born in 1910 into a long-established industrial family and his father, Guenther, was one of Hitler's chief economic advisers. Guenther's second wife, Magda Friedlaender, later married Goebbels and the young Herbert spent part of his youth at the propaganda minister's home.

By the time war broke out in 1939, however, Herbert was already an adult and was no longer in close contact with Goebbels, who poisoned himself, his wife and their six children in Hitler's bunker in 1945.

Much of the Quandt family business was in ruins after the war and a great part of what survived had been commandeered by the invading Soviet forces. The task of rebuilding its fortunes fell mainly to Herbert, who proved to be a highly effective businessman, saving BMW from bankruptcy in 1959 by increasing his stake in the company and unflinchingly selling the family stake in Daimler Benz when he judged the time to be right. This sale set off a tradition of rivalry between BMW and Daimler which has continued to this day and may have contributed to the Bavarian company's present crisis.

Johanna, who had been Herbert's secretary, became his third wife in 1960 and inherited most of his fortune, including his entire stake in BMW, on his death in 1982.

At 72, Johanna Quandt still goes to her office every day in the little town of Bad Homburg near Frankfurt and works there alongside her daughter Susanne (37) and son Stephan (33) until late each evening before returning to the fortified villa where she lives alone. Although she is one of the richest women in the world, with a family fortune estimated at £14 billion (€17.78 billion), she always flies economy class and the only luxury she allows herself is the large BMW she drives.

Johanna was determined from the start that her two children should have as normal an upbringing as possible and when Susanne went to work at BMW, she took a job in the canteen. Johanna and Susanne made the news briefly and unwillingly in 1978 when a last-minute police intervention foiled an attempt to kidnap them. A 14-strong gang led by convicts on day release from the local prison had intended to snatch the two Quandts from their home in broad daylight and demand a £9 million ransom.

This experience may explain the Quandt's extreme aversion to publicity and both Susanne and Stephan are accompanied by bodyguards at all times.

The Quandts have never given an interview to the media and have seldom been photographed.

BMW declines to give details of the extent of the family's involvement in business decisions but Susanne and Stephan sit on the advisory board and Johanna is known to have approved the decision to buy Rover in 1994.

The Quandts were believed to be uneasy about the British venture but went along with the strategy of the former BMW chief executive, Mr Berndt Pitsch etsrieder, for almost six years. It was only when Rover's losses threatened to damage BMW's core business that the family decided that Mr Pitschetsrieder had to go.

The Quandts have been scrupulously loyal to Mr Pitsch etsrieder's successor, Prof Joachim Milberg - in public at least - since the Rover sale. But they have been unable to crush speculation that they are looking for an elegant way to dispose of BMW.

Suspicions about the Quandts' intentions focus on Susanne and Stephan, both of whom went to business school in the United States and are less steeped in the German corporate tradition than is their mother. Mr Gauly denies that the younger family members, both of whom run businesses outside the motor sector, are driven, like most English-speaking investors, by shareholder value.

"Their ideas are closer to the stakeholder concept, whereby the value of a company is not only measured by the index but also by, for example, the question of how a company deals with its employees or how much social responsibility it undertakes," he said.

Mr Gauly also claims that the Quandts are not politically-minded but Johanna has long been friendly with the former German chancellor, Dr Helmut Kohl, and the family contributed almost £1 million to Germany's conservative parties in the run-up to the general election in 1998.

When Chancellor Gerhard Schroder's centre-left government came to power and the former finance minister, Mr Oskar Lafontaine, threatened to squeeze more tax from the rich, the Quandts transferred their stake in BMW to a succession of joint-stock companies. Mr Lafontaine's successor as finance minister, Mr Hans Eichel, has performed a dramatic U-turn on tax and delighted big business by changing the terms under which companies can sell their stake in other firms.

Until now, a decision to sell their stake in BMW would have resulted in a massive tax bill for the Quandts but, from January 1st next, such a deal will be entirely tax-free. Mr Gauly insists, however, that the family has little choice but to hold onto its stake in the company that has proved so profitable for them for half a century.

"If they were to sell it, what should they do with the money? The Quandts are not venture capitalists. They don't know anything about Internet businesses. What they know about is the motor industry," he said.