Johnson & Johnson knew that its talcum powder contained asbestos but failed to tell customers for over three decades, an investigation has found.

Shares in the company plunged 12 per cent following the release of the report by news agency Reuters, wiping £37bn ($47bn) off the company's value.

The investigation also found that the pharmaceutical company had employed a range of tactics to shape research into the problem and protect its Baby Powder brand.

In one case, the company commissioned and paid for a study, told the researchers their desired results and then hired a ghostwriter to redraft the article presenting the findings.

The investigation centres on a cache of documents released by Johnson & Johnson relating to the 11,700 plaintiffs claiming that the company’s talc caused their cancers.

The documents show that from at least 1971 to the early 2000s, the company’s raw talc and finished powders sometimes tested positive for small amounts of asbestos, and that company executives, mine managers, scientists, doctors and lawyers fretted over the problem and how to address it while failing to disclose it to regulators or the public.

A case in July, in which a judge ordered the company to pay $4.69bn in damages to 22 parties, was the first to succeed with a claim that the talc caused ovarian cancer.