New documentary evidence about a pregnancy test drug linked to thousands of birth defects bolsters claims of an alleged cover-up, an MP has said.
Hundreds of files relating to Primodos, a hormone test prescribed to expectant mothers in the 1960s and 1970s, were uncovered by Sky News at the Berlin National Archive, in Germany, last year.
Among them were findings in January 1975 by the UK's then principal medical officer that women who took a hormone pregnancy test had a "five-to-one risk" of having a child with birth defects.
The test has been officially linked to more than 3,500 women whose babies suffered birth defects, though campaigners believe the figure could be far higher.
Sky News said Dr William Inman, of the Committee on Safety of Medicines, reportedly wrote to the drug's manufacturer Schering, and warned them to "take measures to avoid medico-legal problems" and later that he had destroyed his research to avoid "individual claims" being made.
Meanwhile, a letter from Dr Inman published in the British Medical Journal in April of the same year shows the committee had "through its spontaneous reporting scheme only a small number of reports alleging a possible causal association between 'the use of drugs during pregnancy and the subsequent delivery of a malformed child".
His letter concluded the "preliminary" findings of his research meant there was "little justification" for the ongoing use of such tests when alternatives were available.
The medical regulator was first notified about the potential link in 1967, but did not issue any warning until June 1975.
Labour MP Yasmin Qureshi said an all-party parliamentary group had identified hundreds of potential victims but she believed there could be many more.
"This is only the tip of the iceberg," she told the Press Association.
"I think there's thousands out there who have disabilities as a result of this drug.
"Initially, from what I saw, the Committee on Safety of Medicines seems to have known this drug was causing problems but did nothing, completely nothing.
"It was years and years later before they said it should come off the market."
The Government set up an independent inquiry to look into Primodos in 2014.
Ms Qureshi, a shadow justice minister, has previously criticised a lack of progress of the independent panel's inquiry into Primodos.
Health minister Lord O'Shaughnessy said: "I welcome this investigation, it's vital that 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 on the issue."
Pharmaceutical giant Bayer, which acquired Schering Healthcare in 2006, said there was "no link" between Primodos and birth defects.
The German firm said: "Bayer denies that Primodos was responsible for causing any deformities in children.
"UK litigation in respect of Primodos, against Schering (which is now owned by Bayer), ended in 1982 when the claimants' legal team, with the approval of the court, decided to discontinue the litigation on the grounds that there was no realistic possibility of showing that Primodos caused the congenital abnormalities alleged.
"Since the discontinuation of legal action in the UK in 1982, no new scientific knowledge has been produced which would call into question the validity of the previous assessment of there being no link between use of Primodos and the occurrence of congenital abnormalities.
"Based on the facts and on the law, Bayer does not accept that Primodos was responsible for causing congenital abnormalities."
The Medicines and Healthcare products Regulatory Agency (MHRA) said an expert panel had met five times and heard evidence from families from the Association for Children Damaged by Hormonal Pregnancy Tests (HPTs).
A spokesman said the group would report the findings of its "thorough and impartial" review to the Commission on Human Medicines and an update was expected later this year.
The spokesman added: "Previous reviews have found insufficient evidence to link Hormonal Pregnancy Tests with congenital defects, however this review is the most comprehensive undertaken and is focused on the strength of the scientific evidence for a possible association between exposure in pregnancy to HPTs and adverse outcomes in pregnancy."