Hillary Clinton has intervened in talks over the future of Opel and Vauxhall at the request of German ministers as the American Government unveiled plans to sink more taxpayers’ funds into the European carmakers’ US parent, General Motors (GM).

Frank-Walter Steinmeier, the German Finance Minister, spoke by telephone today with Mrs Clinton to seek "support in the search for a solution," his spokesman said. Mrs Clinton pledged to intervene to demand "the greatest possible American support" from Timothy Geithner, the Treasury Secretary, the spokesman added.

Karl-Theodor zu Guttenberg, the Economics Minister, also denounced the US Treasury for dispatching a junior official who had to consult Washington through a video link at regular intervals during the night.

Mr Guttenberg said the talks had been "absurd in parts" and demanded "more seriousness and a greater willingness to compromise on the part of the US."

It is also hoped that developments today in the US could pave the way for smoother negotiations with the two preferred bidders - Fiat, the Italian car group, and Magna, the Canadian components maker.

GM's biggest bondholders have agreed to a new offer to wipe out the automaker's debt, raising hopes that the carmaker will make a quick exit from the now inevitable move into bankruptcy.

Bondholders that own about 20 per cent of GM's $27.2 billion of unsecured debt agreed to wipe out the borrowings in return for a 10 per cent stake in the company and warrants to buy a further 15 per cent of the equity in the new business.

They had previously rejected an offer of a flat 10 per cent because the United Auto Workers (UAW) union had been promised more equity - 17.5 per cent - for a smaller $20 billion debt.

The remainder of GM's debt investors, which include individuals and pension funds, have until Saturday afternoon to agree to the new offer.

If they do not support the offer, forcing GM into a contentious bankruptcy, the Government has warned that bondholders will be all but wiped out.

In exchange for the improved payout, creditors must agree not to oppose a move to sell GM’s profitable assets to a new company funded by the Government in a fast-track bankruptcy process.

GM's filing also revealed that the Government's stake in the restructured company would be 72.5 per cent, much larger than the 50 per cent it was expected to be handed in return for forgiving some of the bailout cash it has provided the company.

The bigger stake is likely to increase the cost of GM's bankruptcy to taxpayers, which is estimated to reach as high as $50 billion.

Overnight negotiations over the future of the US carmaker’s European operation broke down when GM sought more funding for Opel despite Germany’s pledge to provide billions of euros in state guarantees as well as a €1.5 billion bridging loan.

Lord Mandelson, the Business Secretary today reiterated the British government’s support for Vauxhall but said it was too early to comment on what funding the UK may provide since talks over Opel needed to be resolved first.

He also said that unlike Opel, Vauxhall was not in desperate need of funding.

Lord Mandelson has extracted promises from both Fiat and Opel over the future of Vauxhall and British jobs.

Although the Business Secretary has conceded that GM Europe suffers from excess costs and is selling vehicles into a depressed market, he has made clear that the amount of money that Britain will commit will depend on the level of job guarantees in the medium term and the long term.

“Each of the bids envisages government support, but we are some way off from a discussion about government's role in any commercial outcome to these discussions,” he said.

The assurances represent a significant victory for Lord Mandelson, who has been desperate to make sure that the German Government does not give in to election-year pressure with a pledge to protect domestic jobs at the expense of those in the UK. Berlin’s view is crucial because it is being asked to stump up billions of euros in loan guarantees as part of any deal.

Magna calculates job losses of 9,000 across Europe – 2,500 of them in Germany. However, before a Chancellery meeting last night, Magna hinted that it could shift the production of the Opel Astra from Antwerp, Belgium, to Bochum, Germany. Under that scenario, job losses in Germany would total only 300.

Fiat has promised to cut fewer than 10,000 jobs in GM Europe. That could entail closing an engine factory in Kaiserslautern, Germany. Unions fear that overlapping of Fiat’s products with those of Opel and Vauxhall will mean that redundancies could be much higher than promised.

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