GOVERNMENT officials suppressed evidence that wind farm noise can stop nearby residents from sleeping, according to evidence released to campaigners the day after plans for nine turbines were approved.

Documents obtained under the Freedom of Information Act show officers deleted advice to tighten noise regulations because of the effect on those living nearby.

Mike Hulme, of the Den Brook Judicial Review Group, submitted the request for information two-and-a-half years ago, when he was putting together a case against nine 120-metre high turbines near Crediton.

He finally received the documents last week – the day after a government planning inspector gave the green light to the development.

Mr Hulme yesterday described the timing as "unbelievable".

He said the group's experts were now examining whether they could make a case to challenge the inspector's ruling, in light of the new information.

The Department of Energy and Climate Change (DECC) at first refused to release earlier versions of its 2006 draft report on wind turbine noise, compiled by Hayes McKenzie Partnership (HMP), which also gave evidence to the Den Brook inquiry. They said it was not in the public interest, but the Information Commissioner later compelled the department to comply with the request.

Early versions of the report, which was based on evidence from wind farms in Askam in Cumbria, Bears Down in Cornwall and Blaen Bowi in Carmarthenshire, recommended reducing the nighttime noise limit from 43 decibels, first recommended in 1996, to 38, to protect residents.

It also recommended a "penalty" which would reduce it to 33 if the turbine blades made a beating noise as they rotated, particularly as such noise was found to penetrate walls and disturb sleep.

But the recommendations were deleted after officials questioned how they would be interpreted.

One comment read: "What will the impact of this be? Are we saying that this is the situation for all wind farms, just these [ie. the three wind farms in the HMP study], a % only for people with sensitive hearing, a problem with older turbines – I think we need a sense of the scale of this and the impact."

The draft statement also incorporated a paragraph on the damaging impact on health of losing out on sleep. It read: "A difficulty in returning to sleep will result in tiredness the next day and all the associated descriptions of ill-health which might be associated with a lack of sleep."

The remark was removed after the anonymous official wrote: "This sentence is dangerous and could be read that wind farms cause ill-health which is not the intention."

Yesterday, Mr Hulme said the situation highlighted the "major conflict of interests" within the department. He said: "On the one hand, they are there to promote renewable energies and to try and meet government targets, but on the other hand, they are responsible for guidelines to protect neighbours. They are clearly coming down on the side of promoting the wind industry every time."

He said the Government should recommission research into turbine noise levels "as a matter of urgency", to replace the "discredited" 1996 guidance, which is still in place.

A DECC spokesman said guidance was in place to assist local authorities, who make the decision – although in the case of Den Brook it ultimately went to a planning inspector.

The spokesman said: "The initial decision not to release the information under FOI was made because it is not usual to disclose documents that are still draft. The changes between drafts were made by the consultants, not DECC.

"Wind power remains a big part of our renewable energy policy but of course each application is treated individually and fairly and all concerns are taken into account."