Coffee drinkers have been unknowingly consuming a brew made from beans grown illegally in one of the world's most important natural parks, a WWF report has revealed.

The WWF said beans grown in the Bukit Barisan Selatan national park in Sumatra, Indonesia, were being bought by local traders and mixed with legally grown beans before being exported. The 324,000 hectare park is a world heritage site and one of the few protected areas where three endangered or critically endangered species - Sumatran tigers, elephants and rhinos, coexist.

The WWF said that almost 28% of the forest had been degraded, 60% of that by illegal agriculture. The group's research found that in June 2004 more than 45,000 hectares of park land was being used to produce some 19,600 tonnes of coffee annually. Most wildlife had already abandoned those areas.

If this trend of illegally clearing park land for coffee isn't halted, the rhinos and tigers will be locally extinct in less than a decade.

The report says that most of the companies buying the coffee were unaware of its illegal origins, due to the lack of regulations in the region.Some had denied buying any illegally grown coffee, while others were in talks with the WWF on how to avoid buying the coffee and restore the park's habitats. The charity is asking multinational coffee companies to implement rigorous custody controls to ensure that they are no longer buying illegally-grown coffee and is asking the Indonesian government to better protect the park. WWF said it was also asking the coffee-buying companies involved to provide local Sumatran growers with incentives to switch to sustainable coffee production.