The damning report by a cross-party select committee of MPs came as an embarrassing blow to Jeff Rooker, the agriculture minister, who is pressing ahead with the new safety limits, and cast fresh doubts on the threat to limit the intake of other vitamins such as vitamin C.
The report also threatened to engulf the Ministry of Agriculture in a new controversy over its "nannying" in seeking to protect the public from risks in the wake of the beef-on-the-bone ban.
The findings could lead to a reprieve for consumers who regularly take high doses of the vitamin B6 for a range of problems, including premenstrual tension, and who would have to get a prescription for high doses if the new limits are passed.
The MPs urged Mr Rooker to abandon his proposal to limit the sale over the counter of vitamin B6 to a daily dose of 10mg, and seek a voluntary agreement allowing doses to ten times that limit.
They made an extraordinary attack on the "stubbornness" of the Committee on Toxicity in Foods (Cot), which advised Mr Rooker to set the safe limit at 10mg.
The select committee, chaired by Tory MP Peter Luff, said Professor HF Woods, the chairman of Cot, had responded fully to questions by the MPs but it accused Cot of being "curt almost to the point of rudeness" with consumer objections. Describing Cot's advice as "palpably wrong", the MPs said: "We have been dismayed by the stubbornness and defensiveness which Cot has displayed following serious scientific challenges which have been made to its findings."
The committee said: "The crucial error made by Cot was not to establish clear criteria for evaluating the significance of different research data. It failed to establish criteria for distinguishing between good and bad science."
Cot's advice was based on a study of 172 women attending a private clinic who were found to have raised blood serum B6 levels. A total of 103 of the women complained of neurological symptoms including muscle weakness and numbness.
But the Vitamin B6 Scientific Task Group criticised the study for failing to use an untreated control group. Professor Woods told the MPs the study was weak but consistent with other findings, but the MPs said the doubts about the study were "so serious that it is scientifically unjustifiable to use them as the basis for establishing a lowest observed adverse effect level in relation to vitamin B6 intake".
Professor Woods has been appointed to chair the Expert Group on Vitamins and Minerals to review the use of large doses of other vitamins. There was no direct criticism in the report of Professor Woods, but Chris Whitehouse, of Consumers for Health Choice, which lobbied against the limit, said the report had made Professor Woods's position on the new expert group "untenable".