In fact highly processed and inactive substances which might have originated from bovine materials were sometimes present in finished vaccines, she admitted.

It is the second correction issued by the government this week, after the work and pensions department revealed it has overestimated public savings in private pension schemes by up to £30bn.

Ms Blears apologised to MPs for the inaccuracy, saying it was due to wrong advice given to ministers by the medicines control agency.

Ms Blears stressed that a thorough investigation by experts on the committee on safety of medicines (CSM) had concluded that vaccines did not pose any demonstrable BSE risk.

"The CSM, after an exhaustive and rigorous review, found no source for concern in relation to TSEs about the safety of vaccines used in this country," she told the house.

TSEs, or transmissible spongiform encephalopathies, include BSE and its human version, variant CJD.

Fears about the presence of BSE in vaccines were raised in October 2000 when an oral polio vaccine was recalled as a "precautionary measure".

The vaccine, made by Medeva Pharma, had used material derived from UK calf serum dating back to 1985, when the BSE epidemic was at its height.

Foetal calf serum was regularly used early in the manufacturing process of vaccines. But in the case of the polio vaccine, it was also used in the later stages.

The chief medical officer had concluded that the decision to withdraw the vaccine was correct at the time. However, experts agreed that foetal calf serum had "no detectable infectivity" and the CSM had decided that the risk of Medeval polio vaccine transmitting variant CJD was "incalculably small".

Ms Blears said ministers now had three reports, from the CSM, the chief medical officer, and the Medicines Control Agency, which together provided a comprehensive analysis of the issues relating to TSEs and vaccines.

It was clear from the reports that some statements had been made in parliament which were either incorrect or misleading.

"Ministers made these statements on the basis of incorrect advice and information given to them at the time by the medicines control agency, which licences medicines for the UK market and monitors the safety of medicines in use," said Ms Blears.

"I repeat my apologies to the house and also convey those of my predecessors for the fact that incorrect or misleading information was thus given to parliament, albeit in good faith."

Dr Evan Harris, Liberal Democrat health spokesman, said some questions were still left unanswered.

He said: "Why has it taken nearly two years since the government first suspected that parliament had been misled for the record to be corrected?

"The government has still not said what action it will take against one of the manufacturers of an oral polio vaccine, withdrawn in October 2000, which used UK-sourced bovine material well after this was made unacceptable under government guidelines.

"Liberal Democrats are satisfied, on the information provided, to support the government and the chief medical officer's assertion of the overwhelming benefit of the current vaccination programme compared to any safety risk.

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