The government "is in a muddle" over its plan to ban fizzy drinks in England's schools, a Labour MP says.
New guidelines for schools on food and drink will be introduced next year
Denis Murphy MP is concerned some low-calorie sweet drinks could be prohibited under the proposals, and says some "common sense" is needed.
He has called a Commons debate on Thursday to seek clarification on the proposals from the Education Secretary.
But Ruth Kelly says the new proposals for school food and drink will "end the scandal of junk food in schools".
Mr Murphy says he feels Ms Kelly has been advised by several different agencies with their own agendas.
"I'm sure it wasn't her intention, but some mixed messages have been sent out," he said.
"I want to applaud the government in its efforts to make children eat more healthily, and of course we shouldn't be filling children up with additives, but I really think this is all a bit confused and we risk going overboard.
"Children should have a choice of low-calorie drinks - this is what we should be aiming for," he said.
"But as I understand it some drinks containing quite a lot of sugar will still be allowed, because sugar is considered a more natural product."
He said there was also a question mark over fruit juices made from concentrate and some milk and yoghurt-based drinks.
The subject is being debated in the Commons on Thursday during what is known as an adjournment debate.
After the government's School Meals Review Panel recommended children should have limited access to "unhealthy" foods and drinks, Ms Kelly said crisps, chocolate and fizzy drinks would be banned from school vending machines from next September.
Detailed guidelines will be issued by the Department for Education and Skills in the spring.
But David Charlesworth, deputy managing director of Waters and Robson, which manufactures Abbey Well natural mineral water and flavoured waters, is already concerned.
The company, situated in Mr Murphy's constituency, makes fruit flavoured water which has been approved by 59 local authorities for sale in schools.
However, because it contains sucralose - an artificial sweetener classed as an additive - it could fall foul of the new ban.
"Our drinks came out very well in assessments by the Food Standards Agency because they are low calorie," he said.
"I do think it's absolutely ridiculous that we may not be able to continue to sell them in schools."
A delegation from the soft drinks industry, including Waters and Robson, has been told by DfES officials that drinks containing additives will be targeted by the new guidelines.
"A small number of children do seem to be sensitive to certain additives," Mr Charlesworth continued.
"But they mainly encounter problems with tartrazine, which most soft drinks companies no longer use, or sodium benzoate, a preservative.
"Schools told us they did not want to sell drinks containing saccharin or aspartame, or lots of sugar. We have done a lot of research into sucralose and know it is perfectly safe."
He added that the government's School Meals Review Panel had not understood the importance of providing drinks which hydrate children.
But children would tend not to choose just plain water, he said, so it was important to provide a sweeter-tasting drink.
Fruit juices or milk-based drinks would not provide that same degree of hydration.
Some experts have called the proposed ban "too simplistic", including nutrition expert Dr Dee Dawson, medical director of Rhodes Farm clinic for eating disorders.
She said fat and sweet foods and drinks were essential in moderation as part of a healthy diet, and that children needed to learn to choose for themselves.
A spokesman for the Department for Education and Skills said: "The Secretary of State has already made clear the standards will ensure that chocolate, crisps, and sugary fizzy drinks will be banned from vending machines, and school meals should no longer contain low quality foods high in fat, salt and sugar, reformed or reconstituted foods made from 'meat slurry.'"
He said he expected the new guidelines to emphasise prohibiting drinks which contain very high levels of sugar.