The government is launching its first study into the levels of so-called 'forever chemicals' in the UK population. It said current evidence suggested the possible health impacts associated with PFAS are likely to be limited, but said the strongest links found in large population groups have been to raised cholesterol and lower birth weights. The first results are expected next year.

PFAS (per- and polyfluoroalkyl substances) have been used prolifically since the 1940s and 1950s because they are resistant to water, oil and heat.

It is why they have been placed in thousands of items such as pots and pans, clothing and foams used to fight fires.

But because they do not break down easily in the environment - hence the name 'forever chemicals' - they have raised health concerns in recent years.

Two are already banned in the UK - PFOA and PFOS - because prolonged exposure to them can increase the risk of cancer, according to the World Health Organization.

But the study of PFAS is an emerging field with more than 15,000 types to research.

The UKHSA will take blood and urine samples collected through the existing Health Survey for England to establish baseline levels of PFAS, lead, arsenic, bisphenols, phthalates and flame retardants in the population.

In an exclusive interview with BBC Radio 4's Inside Health, Dr Edward Wynne-Evans, director of radiation, chemicals, climate and environmental hazards at the UKHSA, said there are gaps around "what different levels of exposure mean for an individual's long-term health".

There are growing concerns among people living near sites where there has been contamination from the two known toxic PFAS, and they have chosen to get individual blood tests.

In September, blood tests found "really high levels" of one of the cancer-causing forever chemicals (PFOA) in dozens of people living near a major chemical factory.

But the UK government does not recommend individuals get routine PFAS blood testing because there is no "established clinical intervention" if they have elevated levels, Wynne-Evans said.

"If you are going to do a test where you cannot recommend an action to follow, we would not normally recommend a test." He said that this study would help "build an evidence base to better understand what might be happening".

Speaking before this study was announced, Prof Tony Fletcher from the London School of Hygiene & Tropical Medicine said he believed there is a low level of PFAS in everyone's blood.

"If we tested a random sample of anybody's blood, we would measure [PFAS] in low levels."

"We are not all dying because of this but at higher levels [and in larger populations] they have been associated with adverse health effects." For the two banned PFAS - PFOA and PFOS - the known risks include increased cholesterol, an increased risk of cancer, reduced antibody levels following childhood vaccinations and a range of endocrine effects linked to the thyroid and lower birth weights. "I have met with people living in an area with contamination - they are angry," Fletcher said.

"What I try and explain to them is we have found these causal associations between exposure and effect in studying large populations. Although at an individual level, the chances of you getting some bad disease or some adverse health effect is quite low." He stated the important thing is to stop ongoing exposure, to avoid any long-term effects. Inside Health was produced by Imogen Harper and Tom Bonnett.