BBC Health Reporter Toby Sealey explains why the herb was banned

In two cases, customers have fallen ill after the herb, Aristolochia, was used instead of harmless ingredients with a similar name in Chinese.

They were taking Chinese medicines to relieve skin conditions.

The government has introduced an emergency ban on the importation of Aristolochia in a bid to prevent it being included in other remedies by mistake.

And organisations representing traditional Chinese Medicine Practitioners have agreed to voluntarily suspend the the use of the ingredients in question.

Spot check for danger herb

The government's Committee on Safety of Medicines is also recommending a series of spot checks on products to check they contain no Aristolochia.

A similar situation in Belgium in 1993, in which a slimming product became contaminated with the herb, led to 70 cases of kidney failure.

However, until the emergency ban was brought in by the Department of Health on Wednesday, Aristolochia, an unlicensed medicine, could still be prescribed by doctors.

A spokesman for the Department of Health said that by stopping supplies reaching the country, it was hoped that Aristolochia would not end up in the wrong products.

She urged anyone worried about possible contamination of their medicine to get in touch with the supplier for more information.

Permanent ban could follow

The initial ban, on the import, sale or supply of the herb, is only a temporary one, while the authorities decide whether a permanent ban is necessary.

Aristolochia is one of three herbs that can be used to make an ingredient called "Mu Tong". The other two have no known harmful effects.

But a component of Aristolochia is a known carcinogen as well as causing end-stage renal failure.

"Mu Tong" is often used in preparations to treat eczema, urinary problems, fluid retention or swelling and rheumatic conditions.

Debbie Shaw, an expert on the side-effects of Chinese Medicines, said that responsible practictioners had already stopped using Aristolochia in their preparations.

She said: "I would say that there is no need to panic. People with these preparations should stop using them, then take them back to their practitioner to make sure they do not contain Aristolochia."

She said that Aristolochia had been used in China for thousands of years without any reports of serious side-effects.

Doctors have been warned to ask patients visiting with kidney problems whether they have been taking Chinese remedies.

Homeopathic remedies derived from Aristolochia will not be affected by the ban as experts consider them too dilute to carry any risk of toxicity.