Farmers who are determined to cash in on rising crop prices have ploughed up more than 200,000 hectares of land that had been set aside to curb overproduction.

Official estimates suggest that an area the size of Nottinghamshire has been taken over for farming and conservationists now fear that lucrative cereal crops are pushing out wildlife.

A rise in world grain prices and the European Union’s decision last year to abandon its set-aside policy, which was originally designed to end the days of grain and butter mountains, has resulted in a huge expansion in planting.

The Home Grown Cereals Association said that 13 per cent more land was devoted to cereals this year compared with last year. The price of wheat has risen from £60-£70 a tonne two years ago to £120-£150, although the market remains jumpy.

Gareth Morgan, head of agriculture policy at the RSPB, said: “Set-aside was never supposed to help wildlife but, with so much other land farmed so heavily, it became a sanctuary for many species. In East Anglia, much less uncropped land is visible. We’re now looking at a landscape that is just winter wheat or oilseed rape across large tracts of country.”

He said that the expansion would have had a serious impact on several bird species, including skylarks, lapwings, tree sparrows and yellowhammers. Small mammals such as voles and mice were also likely to be affected.

Chris Skinner, a cereal farmer in Norfolk, agreed that wildlife was under pressure from farming. “It’s adversely affecting a great many farmland species and is another nail in the coffin, especially of the grey partridge,” he said.

John Cousins, head of agricultural policy at the Wildlife Trusts, a federation of conservation charities, said that the Government had to act now to prevent some species falling “to levels it’s impossible ever to come back from”. He said: “We’ve identified close to 400,000 hectares which are under threat. Government figures show that half of that land - an area the size of Nottinghamshire – has been lost and we think that figure has been superseded because people are ploughing up at this very moment.”

The Government has acknowledged that there is “a strong case for taking action” and is considering how to respond.

The National Farmers’ Union, however, is not convinced of the risk to birdlife, and opposed extra environmental conditions on farm subsidies, saying: “To introduce further constraints on arable production in the absence of evidence is unwise.”

Farmers also complain that the increase in wheat prices has made livestock feed more expensive and that rising fuel and fertiliser costs have hit them hard.

Richard George, an economist with the NFU, said: “Oil prices have had a huge impact. It’s not just what you put in your tractor – fertiliser has been hit by rising gas prices.”

He said that rising prices could have the paradoxical effect of pushing some farmers out of business. “We were in an awful position two years ago. No one was making money. Now some will. It will encourage strong businesses to do well and encourage weaker businesses to get out because they realise they aren’t going to make any money.”

Ian Frood, who farms 800 acres of mixed cattle and cereal on the Essex coast, said that he had so far resisted price pressures to disrupt the balance of his land. “I’m not one for tearing out hedges and putting in wall-to-wall wheat. I like wildlife. But if you subject us to extreme economic pressures that’s what we’ll do.”

He said that any profit he made from wheat would be offset by rising costs of fuel, fertiliser and pesticides. “Fertiliser two years ago cost £100 a tonne. This year its £340 and still rocketing.”

He also railed against environmental rules that demand wide unplanted margins around the edge of each field. “Why should I suffer just because I’ve got traditional hedges and ditches?”

Mr Frood expected negotiations to be tense when his rent is reviewed next month. “Because of high prices last year, agents are demanding much higher prices for cereal-growing land.” Such costs “are going to have a quite drastic effect on how we farm”.

He said that farmers like him were caught in a dilemma, exposed to the global market yet unable and unwilling to focus single-mindedly on profit. “We’ve had such volatile prices and we’re not used to it. We’re not traders. That’s not what we’re comfortable with doing.”

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