Schemes are being drawn up to construct five plants in the Humber estuary to convert wheat, oil seed rape and sugarbeet into biofuels.

But last night there were warnings that the region risked increasing global warming and destroying rainforests.

Supporters say the power plants will feed off the excess wheat grown in Yorkshire that is not used for food production – allowing farmers to sell produce that at present goes to waste.

But experts warn that even if farmers start growing wheat on set-aside and grassland fields they will still only produce half the amount needed to power just two of the proposed plants.

With more wheat being required to power biofuels refineries, less will be available for food production – pushing up the price of bread, they say.

And the rest of the raw material, they warn, will be palm oil and soya brought in from abroad – and grown on vast tracts of the rainforest harvested to make way for the new crops.

A new strategy from the Yorkshire and Humber Assembly supports the building of at least two large-scale plants in the region – claiming it would bring significant investment and benefit struggling farmers.

But last night a leading politician warned planners to think carefully before allowing any new biofuel plants to be built in Yorkshire, while academics in the region said the answer lay in dev-eloping a greener, cheaper alternative – but not for a generation.

Colin Challen, MP for Morley and chairman of the all-party Parliamentary climate change group, said: "The assembly should be looking at this with extreme caution.

"If the material is being produced on unused land in the UK using farm waste then that is OK and will have a clear benefit.

"There are clear problems that were not expected three or four years ago, which is why the Environmental Audit Committee has called for a moratorium on new biofuel projects, something I support."

Simon McQueen-Mason, a biofuels expert at York University, said the region could develop one of the world's first second-generation plants, which would be run off plant and household waste, would not require raw material from abroad and would produce a genuinely green fuel.

But he said any such plant would be about 20 years away and unless the region started building first-generation plants now it would not be able to develop the knowledge or expertise needed to move into second-generation technology.

"Producing biofuels at the moment is not very energy-efficient," Prof McQueen-Mason said. "Growing wheat needs fertiliser, which needs a lot of energy to produce, while harvesting with a tractor uses up a lot of fuel in itself.

"The carbon footprint from producing biofuel from wheat is not that much better at the moment than burning petrol. Second-generation biofuels will be much healthier. What's more, we will be able to use the wheat's straw as well as its head, halving the amount needed so not eating into the wheat used for food production."

A spokesman for the RSPB, which is campaigning against biofuels, said: "We are concerned that wildlife-rich set-aside farm land will be scrapped to free up land for energy and food crops, with no measures in place to replicate its environmental benefits.

"We are urging the Government to shelve legislation forcing oil companies to sell more biofuel, until there is proof that this new fuel is truly green."

David Bowe, chairman of the Yorkshire and Humber Assembly regional energy forum, said: "This region has a number of features which make it attractive to potential biofuels developers and biorefineries. These include the Humber ports, good transport connections, local feedstock supplies and an available and skilled workforce.

"However, there are also recognised sustainability issues... including the use of food crops and the effect on food prices. (The strategy's authors) have taken these issues into consideration when putting together their recommendations."