Industrial firefighting foams are an essential part of on-site safety in UK factories. But for decades some of these familiar canisters contained potentially dangerous, toxic chemicals.

File on 4 Investigates discovers that 3M the multi-billion dollar chemical company responsible for producing the chemicals knew about the risks as early as the 1960s because their own internal studies on animals and tests on workers indicated a possible increase in rates of cancer. Despite this, the company failed to warn its workers of the dangers associated with using the foams for decades and was involved in an environmental accident at one of its sites that led to the chemicals being released into a Welsh river.

The programme obtained never seen before documents showing the regulator warning the company it thought it had committed an offence but choosing not to prosecute it.

In 2004, with evidence of the risks to the environment of the two specific forever chemicals PFOS and PFOA, a report commissioned by the government recommended any remaining firefighting foams containing the chemicals be incinerated. But we discover in the years after that companies struggled to dispose of legacy stock of foams, and, appearing unaware of the unofficial advice, discharged them straight into the sewer with no treatment, in one case with permission from the water company.

3M said that the health and safety of its workers and their families were “critical priorities" for the company.

Reporter: Esme Stallard Producer: Anna Meisel Technical Producer: Richard Hannaford Production Coordinator: Tim Fernley Editor: Tara McDermott