Health and fitness guru Carole Caplin was back in Downing Street today to help deliver a protest letter calling for Britain to opt out of a European Union directive outlawing hundreds of vitamins and supplements.

But Ms Caplin, Cherie Blair's former confidante who had her No 10 pass withdrawn after the 'Cherie-gate' affair, stayed firmly on wrong side of the famous door and said there was nothing personal in her decision to join the demonstration.

Standing on the steps of No 10 with Chris Grayling, the Tory MP for Epsom, she said: "I’d be here today if Mickey Mouse were in power."

The Commons is due to debate the controversial directive today, as a court case opens at the European Court of Justice over the new EU health food laws.

The British health food industry, and supporters including actresses Jenny Seagrove and Dame Judi Dench, is fighting measures it says will ban thousands of common food supplements and bankrupt many suppliers.

The rules, due to come into force on August 1, impose strict controls on the growing market in natural remedies, vitamin supplements and mineral plant extracts. Under the Brussels directive, approved by EU governments in 2002, health food manufacturers are given until July 12 this year to submit detailed scientific dossiers proving that their ingredients are safe.

But lawyers for British health food manufacturers and health stores will argue in Luxembourg that the costs of complying are prohibitive for many small firms in the health food sector, which have supplied safe products for years.

Boots, one of the largest suppliers of vitamins and supplements, has however already reformulated its products and says it backs the directive.

In Britain, the European Court judges will be told, the EU legislation threatens 5,000 products containing more than 200 nutrients, long used safely in specialist supplements, but now blighted because they are not on the "positive list" of permitted substances. An action group, Consumers for Health Choice, say 21 million people take vitamins and supplements in the UK, but many of the most natural plant-based supplements will now be banned.

The directive lists only 28 vitamins and minerals, and 112 sources from which they were derived for use in food supplements, which can be sold legally after it comes into force on 1 August.

The plans caused controversy from the start, prompting a petition of more than one million signatures, a letter of protest to Tony Blair from more than 300 doctors and scientists, and motions opposing the euro-law from both Houses of Parliament.

The health food industry launched its legal action in the UK courts, opposing the UK government’s transposition of the EU directive into domestic law. UK judges said the case amounted to a challenge to the Directive itself, and sent the case to the EU judges.

Andrew Lockley, head of public law at Irwin Mitchell, the law firm advising the health food industry, said that the argument reflected a "culture clash" between the UK and continental Europe, where food supplements are less commonly used.

Mr Lockley said: "We argue that the conditions imposed by the directive are disproportionate and contrary to the vital community principle of subsidiarity - decisions being taken at the lowest practicable level, which in this case would mean by competent authorities within member states. They are therefore incompatible with community law".

Legislation on public health issues is normally left to member states, unless EU-wide measures are deemed necessary to protect consumer health. The British health food lobbyists insist there is no widespread consumer welfare issue, and that the new Directive will impose such heavy regulatory costs on suppliers that many will go bankrupt.

They also argue that millions in Britain oppose what they see as curbs on their freedom to choose what they eat.

Challenges to EU Directives are rare, but the same court did overturn in 2001 a proposed sweeping ban on tobacco advertising. The judges in that case said the rules had been introduced on the wrong legal basis, and that measures to protect public health were matters for member states themselves.

No verdict will be announced after the hearing: an interim "opinion" from the European Court’s Advocate-General will be published in the next few months, with the final verdict from the full court likely before the August deadline for the introduction of the contested health food rules.

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