Campaigners are calling for a ban on a colouring linked to cancer which has been found in Coca-Cola sold in Britain.

A chemical in the caramel colouring that gives the drink its distinctive colour has been at the centre of a health alert in the United States.

Coca-Cola has recently switched to a new manufacturing process in America to bring down the level of the suspect chemical, 4-methylimidazole (4-MI).

But this precaution has not yet been taken in other countries such as Britain, where its products are the nation’s biggest selling soft drinks with sales of £1.1billion a year.

The amount of 4-MI found in regular Coca-Cola cans sold in Britain was 135 micrograms – some 34 times higher than the 4mcg level in the US, according to research by the US group Center For Science In The Public Interest in partnership with Britain’s Children’s Food Campaign.

Health authorities in California are so concerned that they have passed a law that requires any can of drink containing a 4-MI reading of 30mcg or more to carry a health warning. If this safety assessment was applied in Britain, all cans of Coke would have to carry a warning.

The contaminant results from the industrial process, involving ammonia, that creates the caramel colouring. Chemical reactions between sugar and the ammonia result in the formation of 4-MI, which has been found to cause cancers in laboratory tests with mice and rats.

The results of the campaigners’ research are to be published in the International Journal Of Occupational And Environmental Health, and today they will write to British health ministers calling for an outright ban on the colouring.

Malcolm Clark, campaign co-ordinator at the lobby group, said: ‘Coca-Cola seems to be treating its UK consumers with disdain. The company should respect the health of all of its customers around the world, by using caramel colouring that is free of known cancer-causing chemicals.

‘The UK Government must regulate to protect public health from companies that aggressively market sugar-laden drinks that lead to obesity, diabetes and tooth decay.’

Manufacturers say it is possible to provide a caramel colour that is totally free of 4-MI, however it is four times more expensive.

The CSPI examined regular Coca-Cola from around the world. In the US the 4-MI level was 4mcg per 355ml. The figure was higher in every other country, from 56 in China to 267 in Brazil. Diet Coke and Coke Zero were not included, but earlier tests suggest they tend to have one third less of the contaminant than the standard drink.

The Office of Environmental Health Hazard Assessment in California, which made the warning labels law, said: ‘Studies published in 2007 by the federal government’s National Toxicology Program showed that long-term exposure to 4-MI resulted in increases in lung cancer in male and female mice.’

California’s experts suggest that regular consumption of 4-MI at its warning label level of 30mcg would cause cancer in one in 100,000 people over their lifetimes.

Coca-Cola strenuously denies there is any human health risk from 4-MI.

It said the decision to change the manufacturing process in the US, made public in March, was to avoid the need to apply ‘scientifically unfounded’ health warnings to cans and bottles.

The British arm of the company said it will change the caramel colouring used in its drinks in this country, but was unable to put a timescale on it.
It said: ‘We intend to expand the use of the reduced 4-MI caramel globally as this will allow us to streamline and simplify our supply chain, manufacturing, and distribution systems.’

The British Soft Drinks Association said there was no need to ban caramel colours containing 4-MI.

A spokesman said: ‘The 4-MI levels found in food and drink products pose no health or safety risks. Outside the state of California, no regulatory agency in the world considers the exposure of the public to 4-MI as present in caramels as an issue.’

The spokesman and Coke said food safety watchdogs in Britain and Europe have both decided the presence of 4-MI in caramel colouring is not a health concern.