Better Plan, Wisconsin

The guidance from consultants indicated that the sound level permitted from spinning blades and gearboxes had been set so high - 43 decibels - that local people could be disturbed whenever the wind blew hard. The noise was also thought likely to disrupt sleep.

The report said the best way to protect locals was to cut the maximum permitted noise to 38 decibels, or 33 decibels if the machines created discernible "beating" noises as they spun.

It has now emerged that officials removed the warnings from the draft report in 2006 by Hayes McKenzie Partnership (HMP), the consultants. The final version made no mention of them.

It means that hundreds of turbines at wind farms in Britain have been allowed to generate much higher levels of noise, sparking protests from people living near them.

Among those affected is Jane Davis, 53, a retired National Health Service manager, who has had to abandon her home because of the noise.

It lies half a mile from the Deeping St Nicholas wind farm in south Lincolnshire whose eight turbines began operating in 2006.

"Our problems started three days after the turbines went up and they've carried on ever since. It's like having helicopters going over the top of you at times - on a bad night it's like three or four helicopters circling around," she said.

"We abandoned our home. We rent a house about five miles away - this is our fourth Christmas out of our own home. We couldn't sleep. It is torture - my GP describes it as torture. Three hours of sleep a night is torture."

The HMP report was commissioned by the business department whose responsibilities for wind power have since been taken over by Ed Miliband's Department of Energy and Climate Change (DECC).

The decision to stick with existing noise limits became official guidance for local authorities ruling on planning applications from wind farm developers.

It has also been used by ministers and officials to support the view that there was no need to revise official wind farm noise guidelines and that erecting turbines near homes posed no threat to people's health and wellbeing.

In 2007 Mike Hulme of the Den Brook Judicial Review Group, a band of residents opposing a wind turbine development close to their houses in Devon, submitted a Freedom of Information request asking to see all draft versions of the study.

Officials refused the request, claiming it was not in the public interest for them to be released. Hulme appealed to the information commissioner's office, which has ordered Miliband's department to release the documents. The drafts show the HMP originally recommended that the night-time wind turbine noise limit should be reduced from 43 decibels to 38, or 33 if they made any kind of swishing or beating noise - known as "aerodynamic modulation".

The HMP researchers had based their recommendations on evidence. They took noise measurements at houses close to three wind farms: Askam in Cumbria, Bears Down in Cornwall and Blaen Bowi in Carmarthenshire.

They found that the swish-swish signature noise of turbines was significantly greater around most wind farms than had been foreseen by the authors of the existing government guidelines, which date from 1996. They also found that the beating sound is particularly disruptive at night, when other background noise levels are lower, as it can penetrate walls.

In their draft report the HMP researchers recommended that "Consideration be given to a revision of the night-time absolute noise criterion", noting that this would fit with World Health Organisation recommendations on sleep disturbance.

However, an anonymous government official then inserted remarks attacking this idea because it would impede wind farm development. He, or she, wrote: "What will the impact of this be? Are we saying that this is the situation for all wind farms ... I think we need a sense of the scale of this and the impact."

The final report removed any suggestion of cutting the noise limits or adding any further penalty if turbines generated a beating noise - and recommended local authorities to stick to the 1996 guidelines.

Hulme said: "This demonstrates the conflict of interests in DECC, because it has the responsibility for promoting wind farm development while also having responsibility for the wind farm noise guidance policy ... meant to protect local residents."

Ron Williams, 74, a retired lecturer, lives half a mile from the Wharrels Hill wind farm in Cumbria. He has been forced to use sleeping pills since its eight turbines began operating in 2007.

"The noise we get is the gentle swish swish swish, non-stop, incessant, all night," he said. "It's like a Chinese torture. In winter, when the sun is low in the sky, it goes down behind the turbines and causes flickering shadows coming into the room.

"It's like somebody shining car headlights at your window ... on and off, on and off. It affects us all. It's terrible. Absolutely horrible."

Lynn Hancock, 45, runs a garden maintenance business. She has suffered disruption since 2007 when the 12-turbine Red Tile wind farm began operating several hundred yards from her Cambridgeshire home.

"Imagine a seven-ton lorry left running on the drive all night and that's what it's like," she said. "People describe it as like an aeroplane or a helicopter or a train that never arrives. It's like it's coming but it never gets here."

Such problems are likely to increase. Britain has 253 land-based wind farms generating 3.5 gigawatts, but this is expected to double or even triple by 2020 to help to meet targets for cutting CO2 emissions.