Britain's Advertising Standards Authority (ASA) said Dairy Crest was wrong to rely on the so-called Oxford-Durham study to claim that its omega-3-enriched, St Ivel Advance milk could enhance children's ability to concentrate and learn.
Dairy Crest has agreed to stop making the claim at the ASA's request, following a complaint from the instigators of the Oxford-Durham Study and from two members of the public.
The ruling is a publicity blow to Dairy Crest, one of Britain's biggest dairy processors, as it attempts to capture more added value markets.
The ASA said in its ruling, published Wednesday, that omega-3 supplements had appeared to help children with learning difficulties in the Oxford-Durham Study. But, it said St Ivel advance did not contain the same ingredients or the same amount of omega-3 as these supplements.
The maker of those supplements, Equazen, complained to the ASA after conducting its own analysis of St Ivel Advance.
Adam Kelliher, Equazen's managing director, said children would have to drink more than five litres of semi-skimmed St Ivel Advance every day to get the same amount of omega-3.
"The campaigns were completely misleading and offered false expectations and hopes to consumers, and particularly parents, that one or two glasses of so-called clever milk would make their child cleverer," said Kelliher.
He said Equazen was concerned about damage to its reputation via the Dairy Crest ads.
Dairy Crest has defended its "clever" St Ivel Advance milk, saying its claim was backed up by scientific evidence.
The product has done well since its launch in May 2005, reaching annual retail sales of £13m after its first year and helping the firm move further into higher margin, added value markets.
Lord Robert Winston, a high profile scientist who took part in the Dairy Crest adverts, joined the company in criticising the ASA.
He said he had examined more than 200 peer-reviewed articles and "there is a very strong case for encouraging parents to give their children more Omega 3". He added that milk was a good means of doing this.
Britain's Joint Health Claims Initiative has approved a generic health claim that foods containing omega-3 benefit heart health, but not learning ability or concentration.