Pharmaceutical firms are accused of breaching the United Nations convention on biodiversity, which states that nations have sovereignty over their own natural resources, by scouring continents for samples of unique materials, from plants to bacteria.

A ground-breaking report identifies numerous materials, taken from Africa to Western laboratories, which have developed and patented products worth hundreds of millions of pounds - from a trailing plant beloved of gardeners across Europe to a natural cure for impotence and a microbe used in fading designer jeans.

In some cases companies accept that their product is based on a traditional source and yet there is no evidence the companies have compensated countries from which they took them.

"It's a new form of colonial pillaging," said Beth Burrows, of the US-based Edmonds Institute, the environmental group that published the report. "We have identified a number of cases that require a lot of explanation. The problem is that we have a world [where companies] are used to taking whatever they want from wherever and thinking they are doing it for the good of mankind."

Mariam Mayet, of the South Africa-based African Centre for Biodiversity, co-authors of the report, said: "There is a total disregard and disrespect for Africa's resources. Our findings were made after just one month of research. Imagine what we could discover with two years of research."

Among the companies named is the British firm SR Pharma, which it says holds patents for a mycobacterium collected in Uganda during the 1970s and used to develop a treatment for chronic viral infections, including HIV.

SR Pharma's final director Melvyn Davies confirmed his company had neither offered the product or financial compensation to Uganda. He said the drug had not made any profits for the company, although it had raised $20m (£11.5m) in funding for research.

"If you pick up a natural substance from the street, does that mean it belongs to the country in which you found it? [Our researcher] just happened to be in Uganda," he said. "The issue is not about where the source was but the work that has been done to develop it. Should Uganda share in the profits that will be generated if [it did not invest in the development]?"

Another company mentioned in the report is the German company Bayer. It says that Bayer acquired a strain of bacteria from Lake Ruiru in Kenya, from which it has developed a drug that helps diabetes sufferers.

The patented drug is usually sold under the name of Precose or Glucobay and has generated at least $380m (£218m) in sales. And yet Kenya has received nothing in return. Bayer spokeswoman Christina Sehnert confirmed the product had been developed from the Kenyan bacteria but said that the drug was a product of biotechnology. She said. "You are not using the original. What has been patented is the bio-tech product."

Also taken from Kenya were microbes discovered in the Rift Valley lakes in 1992 by California-based Genencor International. The microbes were used in the manufacture of enzymes used to give jeans a faded look. The exploitation of Africa's natural resources in this manner breaches the 1992 International Convention on Biological Diversity which protects the fair and equitable sharing of the benefits from the use of genetic resources, according to Arthur Nogueira, a senior official with the convention's secretariat in Canada.

How nations are losing out

* Canadian company Option Biotech has patented seeds of Congo's Aframomum stipulatum for an anti-impotence drug called Bioviagra. A bottle of 24 capsules costs £17.

* A microbe from Kenya's Lake Nakuru is owned by US company Genencor and is used to fade blue jeans. Enzymes of another microbe owned by Genencor are used in Procter & Gamble's global detergent brands. The Kenyan government claims it is not receiving any benefits.

* Tanzania's Usambara mountains are home to the plant Impatiens usambarensis, used by Switzerland-based Sygenta and sold as a hanging basket plant. Sygenta made £85m from it in 2004. The Tanzanian government has had no share in the profits.