THE COMPULSORY use of biofuels to partially power every vehicle in Britain could cause higher levels of greenhouse gas emissions, the Government's top environment scientist warned today.

Professor Robert Watson called for the move - designed to cut harmful carbon emissions - to be postponed while a review of the impact of biofuels is carried out.

The Renewable Transport Fuels Obligation (RTFO) is due to take effect from April 1, when biofuels will have to comprise at least 2.5% of fuel at the pumps.

But Prof Watson, chief scientist at the Department for the Environment, cautioned that there were still doubts about the effects of at least some biofuels.

"Many people still believe that some biofuels are indeed still sustainable from an environmental standpoint," he told BBC Radio 4's Today programme.

"I think we need to check that.

"It would obviously be totally insane if we had a policy to try and reduce greenhouse gas emissions through the use of biofuels that's actually leading to an increase in the greenhouse gases from biofuels."

Biofuels, mainly ethanol and diesel made from plants, have been promoted as an alternative to the use of liquid fuels in transport which account for about a quarter of global greenhouse emissions.

Asked about the April 1 start date for the RTFO, Prof Watson added: "I would suggest that we would indeed wait until the review is completed."

end (reopens) A coalition of Britain's leading environmental and development groups today wrote a joint letter to the Government warning that its biofuels policy risked doing more harm than good.

In a letter to Transport Secretary Ruth Kelly, groups including Oxfam, CAFOD, RSPB, IIED, Friends of the Earth and Greenpeace said "there is a very real risk that the RTFO will make climate change worse, not better".

Doug Parr, chief scientific adviser of Greenpeace, said: "From next month British motorists will be forced to pump biofuels into their tanks with no way of knowing if the so-called green fuels they're using are actually worse for the climate than regular fossil fuels.

"For one of the Government's top scientists to describe these plans as potentially insane suggests that something has gone seriously wrong here.

"The targets should be scrapped. Pressing ahead regardless of the consequences for the climate would be incredibly reckless."

Abigail Bunker, agriculture policy officer of the RSPB, said: "Biofuels threaten untold damage to unique wildlife habitats across the world.

"Their production is already causing the destruction of rainforest, peatlands and grasslands and the release of huge amounts of carbon stored by trees and soil.

"Thousands of people last week urged the government to shelve its plans to force us to buy more biofuel. Ministers must heed those pleas not bulldoze through more biofuel use."

Kenneth Richter, biofuels campaigner at Friends of the Earth, said: "It would be irresponsible to press ahead with volume targets for biofuels in the UK and the EU while there is no scientific consensus about their climate impacts and at a time when experts are still scratching their heads about how to adequately safeguard against their potentially catastrophic impacts on people and the environment."

Robert Bailey, Oxfam's biofuels policy lead said: "The RTFO should be delayed until the Government can guarantee that the UK's biofuels will neither make climate change worse, nor come at the expense of the environment and the livelihoods of people in developing countries."