Children's health campaigners accused the government's School Food Trust yesterday of watering down new regulations aimed at providing healthier drinks in schools after succumbing to pressure from the food industry.

In a U-turn, the trust has agreed to allow children to drink additive-laden "combination" drinks - which combine water, fruit juice and/or milk - in school canteens, rather than restricting them to the nutritionally superior "pure" drinks initially proposed.

The revelation was made by the Children's Food Campaign, which also warned that plans for a voluntary code of practice to regulate the use of additives in school drinks would lead to overwhelming influence by the food industry.

The School Food Trust is justifying the use of flavoured and sweetened milk drinks in particular as a way of getting children to drink more milk to boost calcium levels. The move by the trust - set up to improve the nutritional standards of food and drinks in schools after the TV campaign by the chef Jamie Oliver - comes as the government finds itself under pressure to restrict, and in some cases ban, artificial additives in children's products .

The decision to allow combination drinks follows a meeting of the School Food Trust on June 4 attended by representatives of the drinks industry, including Coca-Cola, Dairy UK and Abbeywell. A follow-up letter to participants explaining the revised policy admits: "In working with the DfES on the development of the school food regulations, one of the most difficult areas was drinks."

Yesterday the trust said the rules on drinks had been changed partly because of new European legislation. Michael Nelson, the trust's director of research, said: "The original intention of the School Meals Review Panel (SMRP) was for children to have 'pure' drinks in schools which offer nutritional benefit. This was embodied in the 2006 legislation. The 2007 standards relating to school drinks have changed for two reasons, however. First, EU legislation does not permit restrictions of a number of additives to drinks which can be sold in schools. Second, the SMRP was keen for children to increase milk consumption to address the lack of calcium in the diet."

But Richard Watts, coordinator of the Children's Food Campaign, said: "The trust has come under great pressure from industry to take this step. It is time for the School Food Trust to bite the bullet and ban additives from all drinks in school."

The government's Food Standards Agency was separately accused yesterday of having a pro-industry bias. The FSA published the results of research last week confirming a link between some additives and hyperactive behaviour.

In a strongly worded letter to Dame Deirdre Hutton, who chairs the FSA, campaigners led by the Soil Association said it had failed to act in the interests of consumers when consulting on its findings.