After Helen Buniak watched her son Lee throw five tantrums in almost as few days she started to keep a meticulous diary of what he was eating.

Buniak, a social worker from London, suspected there might be a link between Lee’s diet and his behaviour. There had been a series of birthdays among his classmates before the tantrums and sweets were given out at each one. Buniak wondered whether there might be a link between the brightly coloured sweets and the mood swings and sudden speech disorders Lee, now 9, had suffered from since he was a toddler.

Buniak kept the diary for two years, at the end of which time she discovered that she was right. If she excluded brightly coloured processed foods, sweets and lurid children’s drinks and lollies from Lee’s diet, he was calm and happy.

“His behaviour has had a terrible effect on normal family life sometimes, and it is very difficult to completely exclude problem foods,” she said. “You can give him a cake containing red jam without knowing the jam has masses of red colouring in, which has a terrible effect on him.”

The first concrete evidence of the damage caused by the lurid petrol-based colourings used in children’s sweets, drinks and other products, is expected to emerge in the next few months.

A major study of children’s diet by scientists at Southampton University, as well as evidence from toxicologists elsewhere, will finally prove that fears about junk food are not just the preoccupation of a handful of neurotic families.

The findings are expected to sweep a cold wind through the processed food industry with supermarkets modifying production to meet the concerns.

There are several dyes derived from coal tar, a byproduct of the pet-rochemical industry, which are used in foods here although they have been banned from most products in countries such as America, Austria and Germany because of evidence they cause cancer.

Such is Britain’s laissez-faire attitude to these coal-tar-based dyes, that some, which have been banned from foods, are still permitted in children’s drugs.

Now, however, leaked data from an unpublished food and behaviour in children study at Southampton University, funded by the Food Standards Agency, indicate that evidence has been gathered to show that these dyes cause essential minerals such as zinc to be excreted from the body.

Zinc is vital to the processing of information by the brain. Numerous studies have shown zinc deficiency is linked to violent behaviour.

The £750,000 study, led by Jim Stevenson, the associate dean of medicine at Southampton University, investigated behaviour changes in three-year-olds and eight and nine-year-olds after they had consumed two different mixtures of E numbers commonly found in foods aimed at children.

The first mixture was E102 tartrazine, E110 sunset yellow, E122 car-moisine and E124 ponceau 4R; the second mixture had E110 and E122 again, E129 allura red, E104 quinoline yellow plus the preservative E211 sodium benzoate.

It mirrored Stevenson’s earlier investigation of the same question in 277 three-year-olds on the Isle of Wight, reported three years ago.

At that time, the toddlers’ parents volunteered to keep them on a special additive-free diet. In certain weeks the children were given a daily drink that either contained the additives or was an identical-looking and tasting fruit drink. Neither the parents nor the children knew which type of drink was being given. It was found the parents reported more disruptive behaviour when the children received the additives.

Clinical tests failed to show behavioural differences, however, and the researchers decided that tests on such young children may not have been sufficiently reliable.

Stevenson has been told not to discuss his latest findings ahead of formal publication, but it is understood the recent study backs up the conclusions of his earlier work – and this time includes evidence from teachers as well as parents.

Other research by Neil Ward, professor of chemistry at Surrey University, has demonstrated a link between zinc deficiency and the synthetic yellow coal tar dye tartrazine, which is widely used in sweets and biscuits, as well as tinned peas. He found that consumption of tartrazine caused a substantial rise in vital zinc being flushed from the body in the urine.

Similar evidence has come from a recent series of Home Office funded studies at Aylesbury young offender institution, which proved that the behaviour of inmates could be dramatically modified if they were fed higher levels of essential nutrients including minerals.

Malcolm Kane, former head of food safety at Sainsbury’s and now a food safety consultant, says coal-tar-derived colourings should be banned. “Their only purpose is to make food cheaper by prolonging shelf life, because they are stable in acids and resist high temperatures,” he said. “They serve no nutrient value to the consumer and there are sufficient question marks over their safety to get rid of all of them.”

However, Tim Lang, professor of food policy at City University in London, believes the power of the food industry lobby will deter the government from seeking a ban on artificial colourings: “What we will get is supermarkets and responsible food producers withdrawing them, but other manufacturers fighting to go on using them,” he said.

For parents like Buniak, a change of policy on the use of the dyes cannot come soon enough. According to Sally Bunday who runs the Hyperactive Children’s Support Group, 75% of hyperactive children have low zinc levels. “There is ample evidence that zinc deficiency is associated with erratic behaviour, depression and aggression,” she said. “We are increasingly worried about bad behaviour among young children in schools. There are plenty of doctors and other healthcare professionals who are aware of this. It baffles me why there is so little interest in examining the bigger picture.”

Sainsbury’s has been quick to pick up on the impending results from Southampton. Last month it announced that it will become the first major supermarket chain to ban artificial colours from its vast range of 120 own-brand soft drinks. The ban will come into force on June 1, and be extended to all other own-brand products “as soon as possible”, a spokesman said.

Judging by the response of the Food and Drink Federation (FDF), the trade body for food manufacturers, however, Lang’s prediction of a tooth and nail fight from other manufacturers seems right. The FDF spokeswoman said colours have an “acknowledged function” in restoring the appearance of food after processing. She claimed that the canning process turns peas grey, and British shoppers would not accept this.

“Much is about consumer perception and expectation. Colours are used to identify flavour – an orange flavour will be coloured orange,” she said. “We have a tradition of colouring foods in the UK which goes back centuries.”