She faced accusations over irregularities and cronyism during a hearing in the European parliament that at times degenerated into near-chaos. MEPs attacked Ms Cresson, commissioner for science and research, over her employment of a friend, a former dentist, as a visiting scientific adviser, and her management of an educational exchange programme now the subject of fraud inquiries by the Belgian authorities.
Mike Tappin, of the British Labour Group, the largest national entity within the Socialists, told Ms Cresson she had created an "atmosphere of illegality and cronyism".
Next month she may face an attempt in parliament to sack her if an independent committee criticises her behaviour.
Yesterday's defection of part of the Socialist group came during a hearing of parliament's budget control committee, which interrogated the former French prime minister on the employment of the ex-dentist, Rene Berthelot, and the administration of the Leonardo youth project.
A French MEP, Jean-Louis Bourlanges, accused Ms Cresson of cronyism; she denied trying to block moves to recoup money from Mr Berthelot for work he never did. He was in place for only a month before having a heart attack but was paid for several more, earning pounds 60,000. "I formally deny that," Ms Cresson said, adding that she had taken "the necessary precautions and acted as soon as we saw changes were needed" in the Leonardo programme.
She faced the embarrassment of having to justify comments last year in which she said problems with the pounds 400m Leonardo project were limited to irregularities. This month the European Commission's anti-corruption unit, Uclaf, referred four dossiers of allegations to Belgian judicial authorities.
Ms Cresson provoked ironic laughter when she said it was often difficult to distinguish between malpractice and fraud. "What is an irregularity and what is a fraud?"Reuse content