A controversial EU directive that could ban thousands of popular vitamin and mineral supplements has been declared illegal by a European Advocate.

The judgment is a victory for health food manufacturers and retailers who appealed to the European Court of Justice to overturn the proposed law.

The new rules governing vitamins and minerals are due to come into effect on 1 August and are designed to improve the safety and efficacy of products sold by the industry, worth millions of pounds. Only named ingredients with proven scientific benefits have been included on an EU "positive" list of approved substances that would be allowed in health supplements.

More than 300 different vitamins and minerals are not on the positive list, meaning that 5,000 supplements will be banned if the proposals become law, according to campaigners, who have been led by Carole Caplin, Cherie Blair's former lifestyle adviser. Popular supplements that will be outlawed include certain vitamin C brands, some calcium capsules and copper tablets.

The legal case against the directive was brought by the Alliance for Natural Health (ANH), a Europe-wide association of more than 300 manufacturers, retailers, consumers and doctors opposed to the legislation.

The advocate general at the European Court of Justice (ECJ) gave an advisory opinion that the directive, as it stands, infringes basic EU principles.

He said that the current proposals lacked clear rules for the European Commission to follow when deciding whether or not to include an ingredient on the positive list. The advocate general's opinion that the directive is "invalid" is not binding, and the full ECJ will rule on the case in July, but the court normally follows his opinion.

More than 20 million people in the UK spend £335m a year on vitamins and supplements in the belief that they bolster health and well-being. One in three women and one in four men takes supplements, and campaigners said the legislation would lead to inferior ingredients being used because more beneficial ones had been left off the positive list.

David Hinde, legal director at the ANH, said: "This is a very significant opinion in a landmark case. What we want to see in the EU is the food supplements directive doing the job for which it was created, which is to provide a 'safe harbour' for food supplements so that they are not classified as drugs, and to promote their availability across the EU. We are optimistic the ECJ will adopt the recommendations of the advocate general."

Under the directive, manufacturers could apply for products to be added to the "positive" list by submitting scientific evidence about the benefits of the supplements. But the high cost of producing such dossiers - up to £250,000 - would have meant that smaller manufacturers and health stores were most at risk from the new rules.

Sara Novakovic, the owner of Oliver's Wholefood Store in Richmond, south-west London, welcomed yesterday's ruling. She said: "At last it is now highly likely that we can continue to offer the products that our customers ask for and want, rather than have to remove them all from the shelves for no good reason and supply them with inferior quality alternatives."

However, the industry faces a continuing fight against EU legislation over health supplements and vitamins. The advocate general upheld the concept of EU legislation on health supplements, saying that the proposals needed to be reworked rather than scrapped.

Further directives on the maximum doses of vitamins and rules governing herbal remedies are due to be brought in over the next two years.

SUPPLEMENTS REPRIEVED?

BORON

A mineral found naturally in nuts, raisins and leafy green vegetables, and included in supplements such as Boots A-Z multivitamins. It is needed for the absorption of calcium, and deficiency is linked to osteoarthritis and osteoporosis.

VITAMIN E

An antioxidant that can protect against free radicals associated with degenerative disease. Naturally occurring versions of the compounds that make up vitamin E would be banned.

SELENIUM YEAST

Antioxidant that can help boost immune response and improve heart function, and is linked to sperm function. Certain types are on the positive list, but yeast form is said to be the most easily absorbed.

IRON

Vital for the production of haemoglobin, the pigment in red blood cells that transports oxygen around the body. Organic forms of iron that are easily absorbed by the body would be banned.

CHROMIUM

A mineral that balances blood sugar levels and is widely used by diabetics to help control their condition. Chromium picolinate supplement, which is not on the "positive list", is seen by health professionals as a safe and effective nutritional supplement for people with insulin resistance and those at risk of diabetes.

CALCIUM

"Bio" forms of calcium that are the most easily absorbed by the body would be banned. Calcium works with vitamin D and is needed to build bones and teeth, and can help regulate heartbeat.

POTASSIUM

A diet low in potassium can be a factor in high blood pressure, and supplements can help with fluid balance, heart rhythm and nerve impulses. More than 20 forms would be outlawed.

SILICA

All forms would be banned, yet it can help maintain flexible joints, supple skin and strong nails and hair. Silica levels in the body deplete with age, and many elderly people take supplements.