The former ministers are accused of causing the deaths or infection of seven people through their negligence in regulating blood supplies, some of which were contaminated with the HIV virus.

Dr Claude Weisselberg, a senior health official formerly responsible for transfusion policy would not testify on Wednesday, saying he himself faces charges in connection with the affair in another court.

His refusal came as the special French court trying former Prime Minister Laurent Fabius and two of his former cabinet ministers heard evidence on one of the most serious allegations.

Alleged delay

Prosecutors are alleging that screening of blood, possibly contaminated with the Aids virus, was deliberately held up for commercial motives.

The charge is that in April 1985 they refused to authorise use of an American blood screening product, known as the Abbot test, to give a French firm, Diagnostics Pasteur, the chance to develop and market its own product.

Reporting from Paris, BBC correspondent Stephen Jessel says that by the time blood screening was introduced in August four months later, several hundred people had received transfusions of contaminated blood.

On Wednesday, the then head of the French firm denied his company had asked for a delay in the introduction of the rival American product and claimed that the French product was also ready in April.

The delay, he said, had been caused by doubts about the cost to the health budget of introducing any tests.

In an important boost for the defence the prosecution seemed to accept that argument.

The BBC's correspondent pointed out that testimony was refused by the one man who might have shed light on the affair, Dr. Claude Weisselberg, the senior official at the Health Ministry in charge of transfusion policy at the time.

The trio face up to three years in jail and a fine of 500,000 francs ($88,000) if found guilty.

Procedural concern

There is mounting concern about the trial, in particular, the performance of the presiding judge and the refusal to give any place to the victims of the affair.