Critics of the government's biofuel policy were given fresh ammunition yesterday after new data revealed that less than a fifth of biofuels used in the UK met environmental standards designed to limit the impact of energy crop plantations on the environment and protect workers rights.

The data from the Renewable Fuels Agency (RFA) showed that biofuels accounted for 2.14 per cent of UK road fuel during the first half of the year, just short of the 2.5 per cent target.

However, only 19 per cent met environmental standards designed to limit deforestation, soil and water degradation and damage to biodiversity, and protect workers and land rights, compared to a target of 30 per cent. Moreover, the RFA admitted there were significant gaps in the data with the original feedstock used only known for 90 per cent of biofuels and the country of origin known in 57 per cent of cases.

The agency said that based on the incomplete data it had calculated that greenhouse gas savings of 42 per cent compared to conventional fuels, but it admitted that this figure excludes emissions resulting from indirect changes in land use, whereby farmers previously growing food on land converted into energy crop plantations engage in forest clearance to open up fresh land.

Repeated studies have shown that this knock on impact on land use has contributed to food price rises and undermined the environmental benefits associated with biofuels, with some researchers claiming that where plantations result in deforestation biofuels can prove more carbon intensive that conventional fuels.

Asad Rehman, Friends of the Earth's biofuels campaigner, said that the data exposed the government's failure to live up to its recent commitment to ensure biofuels meet high environmental standards and deliver verifiable carbon savings. "The shocking admission that we are unable to identify the origin of nearly half the biofuels used in the UK means that the Government cannot assure the British people that the biofuels in their petrol tanks have not destroyed rainforests," he said.

However, the RFA's Chris Malins defended the figures, insisting that good progress was being to ensure that biofuels deliver promised environmental benefits. "This type of data capture has never been done before," he said. " We've made a very positive start and suppliers are taking their reporting obligations seriously… they know the government intends to bring in mandatory environmental standards from 2011 so they are aware of the need to start reporting as soon as possible."

He added that the RFA was still confident that the full year target of ensuring 30 per cent of biofuels meet environmental standards could be met and insisted that the target would increase year-on-year up to 2011.

In related news, the US government delivered a major boost to the biofuel sector after rejecting Texas' request to halve the national ethanol target. The state had requested that the target be cut, claiming that it was contributing to record food prices as growing numbers of farmers switch to producing corn for ethanol producers.

However, the Environmental Protection Agency rejected the request claiming the target "is not causing severe economic harm" and is helping to bolster US energy security.