Pressure on retailers, food companies and biofuel producers to ensure that the palm oil they buy comes from legal and sustainable sources stepped up another notch today with the publication of a new report linking growing demand for the crop to forced evictions, intimidation and even paramilitary murders in Colombia.

The report from anti-poverty lobby group War on Want claims that Colombia's armed forces are colluding with right wing paramilitary groups in the killing of hundreds of Afro-Colombians and the displacement of thousands more to make way for palm oil plantations.

The group claims that UK accounts for almost half of Colombia's exports of palm oil and as such many UK firms are indirectly contributing to the land clearances.

"The Colombian government and the paramilitaries are profiting from the scramble for biofuels while people who stand in their way are murdered and dispossessed," said Gemma Houldey, War on Want's international programmes officer for conflict zones. "Some products bought in Britain could well contain ingredients which results from this brutality."

The findings echo a similar Greenpeace investigation late last year which claimed that a raft of multinationals, including Nestle, Unilever, and Procter & Gamble, were guilty of sourcing illegal palm oil plantations in Indonesia that have contributed to deforestation, destruction of biodiversity and forced land clearances.

The criticism has prompted significant new commitments from a number of palm oil purchasers. Sainsbury's committed last year to begin phasing out palm oil that had not been officially certified as legal and environmentally sustainable by industry group the Roundtable on Sustainable Palm Oil. That commitment was followed earlier this month by a similar pledge from food giant Unilever, which said it too would begin sourcing certified palm oil as it attempts to ensure it can trace the origins of all the palm oil it uses in Europe by 2012.