Traces of a cancer-causing chemical have been found in British soft drinks at eight times the level permitted in drinking water, BBC News has learned.
Benzene levels are limited to one part per billion UK water ( pic by freefoto.com)
The Food Standards Agency watchdog says these do not pose an immediate health risk, but questions need answering.
Benzene, which can cause certain cancers, is thought to be formed when two commonly used ingredients react.
The results came in industry tests prompted by the FSA after the chemical was found in tests on drinks in the US.
These American results were passed by the BBC to the FSA which then asked firms to carry out the tests.
The industry tests on 230 different products revealed levels of up to eight parts per billion in some soft drinks - although the brand names have not been revealed.
Although there is a legal limit of one part per billion on the amount of benzene allowed in drinking water, there are no UK restrictions on the amount of the chemical permitted in soft drinks.
The soft drinks industry has known for 15 years that the preservative sodium benzoate can produce benzene if mixed with ascorbic acid - more commonly known as Vitamin C.
And experts and consumer groups are asking why the two chemicals are still present in so many drinks.
Benzene has been linked to leukaemia and other cancers of the blood and is also found in pollutants such as car exhaust fumes.
Dr Andrew Wadge of the Food Standards Agency said: "The levels found so far are not a cause for concern.
"Let's have further investigations and regular discussions with the drinks industry and check what's happening.
"If levels are high then the FSA will take action to protect consumers."
Dozens of high street brands contain both sodium benzoate and ascorbic acid, which can create benzene if mixed, but the British Soft Drinks Association insists the levels produced pose no risk to health.
Its spokesman Richard Laming said the levels found in soft drinks were very low and at the limits of detectability, and that there was nothing to worry about.
"There is an obligation on industry to have as low a level of benzene as possible and we are looking at ways of reducing the levels - and maybe even removing the preservative - if we can replace it with something else."
He added that someone living in an urban city consumed, on average, 400 micrograms of benzene from exhaust fumes in a normal day.
This would be the equivalent to consuming 40 litres of a soft drink containing benzene at just over the World Health Organization guideline level of 10 parts per billion, he said.
'Right to know'
Professor Glenn Lawrence of Long Island University said the combination of sodium benzoate and vitamin C was commonly found in some drinks in the early 1990s.
Research he published in 1993 revealed how the carcinogen could be formed when these two chemicals react.
He suggested that drink firms were now putting vitamin C back into drinks to encourage consumers to buy the product.
Children's food campaigner Richard Watts of Sustain, a pressure group lobbying for better food and farming, said many of these drinks were being marketed as health drinks to children.
He said parents and consumers had a right to know what was contained in these drinks.
"As I understand it, the scientific evidence is unclear about whether there is any safe level of benzene.
"We would like to see regulations come in about this and we see no reason why it should be different from the designated safe level in drinking water.
He added: "If it's unsafe in drinking water, why should it be safe in soft drinks?"