The growing opposition to the UK's biofuel targets gained fresh impetus yesterday after the government's new chief scientific advisor admitted there were "real problems" with the sustainability of biofuels.

In his first major speech since taking the post, Professor John Beddington told the Govnet Sustainable Development UK Conference that some of the biofuels currently being used are "hopeless" and warned that booming demand for fuel crops could lead to severe global food shortages over the coming years.

"It is very hard to imagine how we can see a world growing enough crops to produce renewable energy and at the same time meet the enormous increase in the demand for food which is quite properly going to happen as we alleviate poverty, " he said.

Beddington warned that the combination of population and economic growth means that there is an urgent need to increase food production globally, a task he said is being made all the harder by the current vogue for biofuels.

Beddington also endorsed environmentalists' fears that many biofuels are delivering limited carbon emission reductions and in some cases are even exacerbating climate change. "In terms of biofuels there has been, quite properly, a reaction against it," he said. "There are real problems with unsustainability… Some of the biofuels are hopeless. The idea that you cut down rainforest to actually grow biofuels seems profoundly stupid."

The comments appear to put the new chief scientist on a collision course with the government, which continues to regard biofuels as a central plank of its renewable energy strategy.

Under its Renewable Transport Fuel Obligation (RTFO), five per cent of fuel at the pump will have to come from biofuels by 2010, while EU targets for 2020 will require 10 per cent of transport fuel to come from renewable sources.

Friends of the Earth biofuels campaigner Kenneth Richter said that Beddington's concerns further strengthened the case for a moratorium on such targets.

"The government’s chief scientific adviser is absolutely right to raise concerns about the role biofuels are likely to play in pushing up food prices," he said. "They will affect prices directly when food crops like corn and palm oil are used to produce biofuels. And indirectly by competing with food crops for land and water resources. The government must wake up to this threat, put its Renewable Transport Fuels Obligation on hold and demand a moratorium on the EU biofuel targets."

The Department for Transport recently acknowledged concerns about the environmental sustainability of such biofuels, commissioning a report into the wider economic and environmental impacts of biofuels.

However, despite calls from green groups for an immediate moratorium on biofuels a spokesman for the Department for Transport said that it would stand by its current biofuel targets at least until the report is published at the end of the year. "We take this issue very seriously and we are not prepared to go beyond current UK target levels for biofuels until we are satisfied it can be done sustainably," he added.