Campaigners for Britain's millions of vitamin and supplement users have reacted with dismay to a ruling that could sweep up to 5,000 products off the shelves.

The European Court of Justice has rejected British health food industry claims that the proposed Food Supplements Directive, coming into force on 1 August, breaches EU rules. Yesterday's decision means some 300 nutrients and nutrient sources in the UK will be banned unless they can obtain inclusion on a "positive" list - a move that supplement manufacturers say requires excessive levels of testing and red tape.

Among the vitamins and supplements facing a ban are boron, important for healthy teeth and bones; sulphur, important for healthy skin; and 1,000mg Vitamin C tablets. The surprise decision of the European Court goes against an opinion delivered by the same court's advocate-general in April, who said the directive was "as transparent as a black box".

British ministers came under pressure yesterday to negotiate an opt-out from the directive. Opposition parties attacked the Government for failing to defend British consumers' interests, saying the decision was a defeat for common sense and an "unwarranted intrusion by the EU into people's lives".

Simon Burns, a Tory health spokesman, said: "The ruling is a devastating blow for thousands of people who regularly use food supplements and vitamins. It is an absolute disgrace that the Government signed up to the directive in the first place. Now that the UK holds the EU presidency, it is imperative that the Prime Minister intervenes swiftly to secure a British opt-out."

Steve Webb, the Liberal Democrat health spokesman, said: "There is no reason why governments should not be able to allow their own consumers to use products which do not have Europe-wide approval."

The consumer organisation Which? defended the decision. Sue Davies, its chief policy adviser, said: "It'll ensure products are safe, that they contain forms of vitamins and minerals that offer some benefit, and that they are clearly labelled."

Caroline Flint, the Public Health minister, said the safety of food supplements had to be balanced against the need to support consumer choice and that "flexibility" should be built into the system. But she added: "We are concerned that some of the provisions in the directive could be unduly burdensome."

Jenny Seagrove, the actress, who has campaigned against the directive, said: "It is shocking news. This is aboutmoney. The opinion of the advocate general, who was scathing about the directive, and Tony Blair, who criticised it, and 300 doctors and scientists and one million people who signed a petition against it can't all be wrong. I wonder what happened with the 12 men in the European Court of Justice and what pressures they were under."