A European Commission official chosen to lead the commission's anti-trust case against Microsoft has asked to work instead for a consultancy that has the software firm as a client, the company and commission confirmed this week.

The commission, whose competition commissioner is Neelie Kroes, is in a court fight with Microsoft over a 2004 decision by Brussels that the company violated EU anti-trust law.

Microsoft was fined €500 million at the time and another €281 million this year for defying the earlier order.

Henri Piffaut, who is French, was due to take over a commission anti-trust unit handling Microsoft and other high-profile technology cases in October, according to more than a dozen sources inside and outside the commission.

But he has instead sought leave to work for LECG, an economic consultancy in Brussels, London and other cities that counts Microsoft as a client.

"A request for leave on personal grounds has been made, but no decision has yet been made on that request by Piffaut," commission spokesman Jonathan Todd said.

Piffaut's request to leave the commission has delayed the process of replacing the departing head of the technology unit handling the Microsoft and other high-profile technology cases.

Todd said that commission officials who leave the EU's executive or take personal leave must agree to strict measures so that there is no conflict of interest in their work.

"Officials may be required to desist from contacts with the commission and may be required to desist from working for or on behalf of companies that have been subject to cases on which the official has worked whilst at the commission," he said.

Todd did not say where Piffaut was going, but LECG's director of competition policy for Europe, Atilano Jorge Padilla, said: "We are interested in hiring him, but he has to sort out a number of things with the commission."

Padilla said no contract had yet been signed with Piffaut, who was being sought for his expertise on mergers rather than antitrust cases such as Microsoft.

Piffaut would lead the economists in the Brussels office, and help hire additional staff.

Padilla, like Todd, said Piffaut would be banned from any work on Microsoft or other cases on which he had worked for the commission. LECG employs more than 40 economists in London, Brussels, Paris, Madrid and Milan.

The European Commission's technology unit has been led for seven years by Cecilio Madero Villarejo.

But this week, the European Commission promoted him to serve as head of the directorate dealing with services, including financial services and transport.

The case resembles one in 2002, when European Commission Information Society director-general Fabio Colasanti permitted a head of unit, Detlef Eckert, to work for Microsoft itself.

Eckert had interviewed a number of Microsoft rivals who had complained about the software giant's behaviour.

At the time, Colasanti said Eckert had "pledged to respect the commission's statutory obligations for what concerns conflict of interest".