The FSA now says hyperactive children might benefit from fewer additives.
But experts said drugs rather than diet changes could improve behaviour more effectively in the most severe cases.
He did say though there were many factors associated with hyperactivity including genes, being born prematurely, environment and upbringing.
Emma Hockridge, of the Soil Association, said the FSA should be taking a leading role in addressing the issue by undertaking initiatives to prevent the development of hyperactive disorders, through new policies to limit food additives.
The Food Commission called on food manufacturers to voluntarily remove additives from their products.
A spokesman said: "These artificial colourings may brighten up processed foods and drinks but it appears they have the potential to play havoc with some children's behaviour."
Julian Hunt, from the Food and Drink Federation, said they accepted the FSA's advice but said the tests did not represent how additives were used normally.
"Manufacturers are very aware of consumer sensitivities about the use of additives in food and drink products. It is important to reassure consumers that the Southampton study does not suggest there is a safety issue with the use of these additives."
This is not the first study to make a link between additives and hyperactive behaviour, but a wider age range of children were selected than in previous research, and not all had behavioural problems.
The Food Standards Agency paid for Southampton University researchers to examine whether giving additives to a group of ordinary three-year-olds and eight or nine-year-olds had any effect on their behaviour.
The children were randomly given one of three drinks, either a potent mix of colourings and additives, a drink that roughly matched the average daily additive intake of a child of their age, or a "placebo" drink which had no additives.
Their hyperactivity levels were measured before and after the drink was taken. Mix "A", with the high levels of additives, had a "significantly adverse" effect compared with the inactive placebo drink.
Dr Jim Stevenson, Southampton University
Lead researcher Professor Jim Stevenson said the study, published in the Lancet, showed that certain mixtures of artificial food colours, alongside sodium benzoate, a preservative used in ice cream and confectionary, were linked to increases in hyperactivity.
He added: "However, parents should not think that simply taking these additives out of food will prevent hyperactive disorders.
"We know that many other influences are at work but this at least is one a child can avoid."
He said it was not possible to say which of the ingredients in the additives cocktail affected the children.
Between 5% and 10% of school-age children suffer some degree of ADHD - attention deficit hyperactivity disorder - researchers suggest, with symptoms such as impulsiveness, inability to concentrate and excessive activity.
More boys than girls are diagnosed with the condition, and children with ADHD can struggle academically, often behaving poorly in school.
Andrea Bilbow, of ADDISS
While more than half had reported some improvement, this tended to be modest when compared with the effect of medication, she said.
"In some respects the question of food additives is a little bit of a red herring.
"While in some cases, a poor diet could make ADHD even worse, a better diet is not going to make it much better," she said.
And Dr Paul Illing, of the Royal Society of Chemistry, raised questions about the validity of the study, saying extrapolating from the small study population to the general public was very difficult.
Irn-Bru is known for its bright orange colour. As of 1999 it contained 0.002% of ammonium ferric citrate, sugar, 32 flavouring agents (including caffeine—though caffeine is not listed as an ingredient on the Australian labelling—and quinine) and two controversial colourings (E110, E124). On 27 January 2010, A.G. Barr agreed to a Food Standards Agency voluntary ban on these two colourings although no date has been set for their replacement. The beverage is advertised as having a slight citrus flavour.
Irn-Bru was first produced in 1901, in the town of Falkirk, under the name Strachan's brew. In 1946, a change in laws required that the word "brew" be removed from the name, as the drink is not brewed. The chairman of the company came up with the idea of changing the spelling of both halves of the name, giving the Irn-Bru brand. 1980 saw the introduction of Low Calorie Irn-Bru: this was re-launched in 1991 as Diet Irn-Bru and again in 2011 as Sugar Free Irn-Bru. The Irn-Bru 32 energy drink variant was launched in 2006.
It has long been the most popular soft drink in Scotland, with Coca-Cola second, but recent competition between the two brands has brought their sales to roughly equal levels. It is also the third best selling soft drink in the UK, after Coca-Cola and Pepsi, outselling high-profile brands such as Fanta, Dr Pepper, Sprite and 7-Up. This success in defending its home market (a feat claimed only by Irn-Bru, and Inca Kola) has led to ongoing speculation that Coca-Cola, PepsiCo, Inc. or its UK brand franchisee Britvic would attempt to buy A.G. Barr.
Irn-Bru's advertising slogans used to be 'Scotland's other National Drink', referring to whisky, and 'Made in Scotland from girders', a reference to the rusty colour of the drink; though the closest one can come to substantiating this claim is the 0.002% ammonium ferric citrate listed in the ingredients.
A limited edition Irn Bru was released in Autumn 2011. Packaged with a black and orange design, and with the signature man icon with a added image of a fire, 'Firey Irn Bru', had a warm, tingly feeling in the mouth once drunk. The after taste to it is similar to ginger but still has the iconic Irn Bru flavour.