A pregnancy test pill given to more than a million British women in the 1960s and 1970s may have caused severe birth defects and life-threatening abnormalities in thousands of cases, a shocking investigation has revealed.

Damning new evidence exposes the scale of the growing scandal and an alleged cover-up over Primodos super-strength hormone tablets, given to women by GPs, the Daily Mail reported.

A review of archived documents found a study by renowned Professor Bill Inman, who was responsible for helping to revise medication safety regulation following the thalidomide scandal. He concluded that the 1.5 million women given Primodos were five times more likely to have a disabled child than those who didn't take the drug.

The findings have renewed hope for the affected families, who have so far not been compensated by the drug's manufacturer. And last week Health Minister Lord O'Shaughnessy announced the Government had ordered medical chiefs to investigate, saying: "It's vital we take concerns such as these seriously. That's why we've asked the Medicines and Healthcare products Regulatory Agency to conduct a thorough scientific review of the evidence."

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Prof Inman's research, carried out in 1975, three years before the pills were eventually withdrawn from the market, was only passed to the drug's manufacturer, German pharmaceutical firm Schering, and not made public.

The investigation also reveals that the potent hormone pills were never tested - even on animals - before being given to women.

The latest revelations, following a lengthy Sky News investigation, are to be broadcast on Sky Atlantic on Tuesday in the documentary Primodos: The Secret Drugs Scandal.

In it, campaigners, who have spent years fighting for a public inquiry into the scandal and justice for the thousands of victims and their families around the world, claim they were used as "guinea pigs".

Drugs giant Bayer, which took over Schering in 2006, continues to deny Primodos caused deformities in children. But Robin Hayes, founder of the campaign group Association for Children Damaged by Hormone Pregnancy Testing, whose son Sean died aged ten after being born with serious defects, said: "I am convinced, and I will be until my dying day, that this drug was responsible for the death of my child."

Primodos was introduced in 1958. Before this, to confirm a pregnancy, a sample from a woman had to be sent to a lab where, bizarrely, it was injected into a toad. If the toad produced eggs in response to the high levels of hormones, it meant the patient was expecting.

Primodos contained high levels of synthetic progesterone, a hormone that helps maintain pregnancy. Women were told they were pregnant if they did not bleed after taking the tablets. But some of them suffered miscarriages and others had babies missing limbs, or with serious heart defects and other physical deformities. The drugs contained 40 times the dose of a contraceptive pill and 30 times that of a morning-after pill.

Researchers found Primodos pills were used regularly for abortions in countries such as South Korea.

Campaigners believe the extent of the defects unborn babies suffered depended on when the pill was taken during pregnancy, and the precise stage of development.

The alarm was first raised in 1967, but it was eight years before warnings were placed on packaging, and ten years before the medication was withdrawn.

A damages claim was launched in 1982 but dropped over fears that victims would struggle to prove Primodos caused the malformations.

The extent of the defects unborn babies suffered could depend on when the pill was taken during pregnancy. photo / Getty Images
The extent of the defects unborn babies suffered could depend on when the pill was taken during pregnancy. photo / Getty Images

The documentary also found evidence of "a collusion" between Schering and the British regulatory authorities. A study by the Royal College of GPs, part-funded by Schering, linked the drug to birth defects in 1969 and recommended it be withdrawn.

But this was passed to the manufacturer, and not to the victim's families for legal action, a decision the RCGP said followed "due practice". Marie Lyon, chair of the campaign group, described the revelation as 'morally indefensible'.

Karl Murphy, 43, was born with multiple deformities he believes were caused by Primodos. He had a cleft palate rectified as a baby but has been left without some fingers, others that stop at the knuckle, and no toes on his left foot.

Karl, from Liverpool, re-formed a campaign group for families - disbanded following the failure of the 1982 legal case - after finding boxes of documents on Primodos in his mother's attic in 2011. All of the damning documents have been handed to the Government's expert working group on Primodos, which meets on March 27. Its findings will be published later this year.

In a statement to the documentary, Bayer says Primodos was on the UK market "in compliance with prevailing laws" at the time. Bayer rejected any suggestion that evidence was concealed and said evidence that the drug caused birth defects was "extremely weak".