A scientist with a leading role in the decision over whether food additives are damaging children's behaviour is also a paid consultant to Tesco and Unilever, companies whose brands use the chemicals under suspicion.

Food policy experts and MPs say the dual role of Dr Sue Barlow, who chairs the European scientific panel assessing the risk of additives, raises serious questions about her suitability to perform such a crucial role. The panel will advise the European Commission on whether to ban the controversial additives, which include a series of E numbers.

It comes after a new study raised fears that a combination of colourings and preservatives commonly used in cakes, drinks and sweets are making children more unruly and aggressive.

Tim Lang, professor of food policy at City University, said: 'Parents who are worried about these artificial additives will look at the decision her committee makes and wonder how reliable it really is. Of course, there is a role for people in industry, but to have someone with such a clear manufacturing and retailing interest in the chair, however much integrity she has as a scientist, sends out completely the wrong signal.'

Barlow, a toxicology expert, will chair a meeting of the additives, foods and chemicals panel of the European Food Standards Authority (Efsa) in two weeks' time. Partly funded by the British taxpayer through the Food Standards Agency, the panel's task is to advise the European Commission on whether there is a clear risk that additives contribute to hyperactive behaviour in children.

It follows a study at Southampton University, published in The Lancet, which found that children without a history of hyperactive behaviour became unruly and impulsive after consuming a cocktail of colourings which use a particular preservative, sodium benzoate.

Some companies, such as Cadbury Trebor Bassett, are beginning to remove the chemicals, but they are still widely used in thousands of products, particularly those targeted at children.

In May 2006, the panel rejected the argument that there might be a link between the sweetener aspartame and cancer. MEPs complained about the role of Barlow, who at that stage worked for the International Life Sciences Institute, a body funded by sweetener manufacturers and major aspartame users such as Coca-Cola, PepsiCo, Nestle and Monsanto. Barlow had been an observer, not chairwoman, at the aspartame meeting, Efsa said. Aspartame is not one of the chemicals currently under investigation.

Barlow said: 'My interests are fully declared, they can be seen by everyone on the Efsa website. I am an employee of Efsa and it is for them to decide whether they represent a conflict of interests.'

She added: 'I can understand why people ask that question, as I am a consultant to Tesco, but Tesco markets food right across the board. My role is to advise them on chemical problems, nothing to do with which products they use.'

Barlow said that she had given advice on additives and had spoken to Tesco about the Southampton study. 'From our [panel's] perspective, it's important to review this study in the context of all the previous work that has gone on - we can't just take it in isolation. We have to establish that there is something there. Do we consider that the reported behavioural changes in children have been well demonstrated or not?'

A Tesco spokeswoman said: 'Susan Barlow is an independent consultant and an expert on toxicology whose work is well recognised. Any suggestion that such a professional would be influenced by Tesco is complete nonsense. As you would expect, we work with many independent experts from the food industry and we all have the same aim, which is to ensure food safety for our customers.'

A spokeswoman for Efsa, which is based in Parma, Italy, said: 'If Dr Barlow is chair of the meeting, then it must mean that there is no conflict of interest.'

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· Additional reporting by Joanna Tomlin