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Michael Sovern, Emeritus Professor of Columbia University, and more importantly a former chairman of the Commission on Integrity in Government, will replace Mr Taubman, while Mrs Brooks' position has gone to William Ruprecht, managing director of Sotheby's North and South America since 1994.

“My decision is a very difficult one, but I have taken it in the best interests of the company and my colleagues,” said Mrs Brooks, offering no further reasons for her resignation. However, in an adjunct to her statement, Sotheby's admitted for the first time to involvement in the anti-trust investigation into alleged commission fixing, saying that it had “recently met with the Department of Justice in order to discuss a prompt and appropriate resolution of this investigation, which will allow the company to put this difficult matter behind it”.

Christie's had already met with the Department of Justice following the resignation of its chief executive Christopher Davidge on Christmas Eve, and offered to co-operate in return for conditional amnesty in any criminal proceedings. However, it is unlikely that Sotheby's would be offered the same terms, as only the first party to come forward with evidence is entitled to enter the “corporate leniency” programme operated by the anti-trust division.

According to reports in the New York Times, the departures “appeared to be an effort to close the door on past practices and fight to maintain a corporate image of integrity”. Sotheby's A share price dropped a further 100 points to 1125 within a day of the announcement of the resignations. Mr Taubman and Mrs Brooks continue to hold respectively the largest and third largest number of shares in the company and both have retained their seats on the board.

While the art world waits to see whether or not the criminal investigation will be resolved in a “prompt and appropriate manner”, civil proceedings entered a new phase as at least 38 class-action law suits filed by clients of both Sotheby's and Christie's are scheduled to be heard before Judge Kaplan in Manhattan Federal Court.

As with the criminal proceedings, the law suits are expected to focus on alleged collusion between both auction houses in upping their buyer's premiums to 15 per cent on the first £30,000 within weeks of each other in 1992, and fixing identical rates for sellers of goods priced between £60,000 and £3m in 1995. Litigation against Sotheby's and Christie's may not only be confined to America. London dealer David Mason has been reported as gathering a consortium of 25 leading dealers and collectors to pursue both auction houses through the European Court in Strasbourg with the aim of overturning the imposition of the buyer's premium.

Meanwhile, investigations into alleged anti-competitive practices by both Sotheby's and Christie's, which between them control 95 per cent of the world auction market, are being conducted by the European Competition Commission, the UK Office of Fair Trading and authorities in Australia.