By Alex Kirby
BBC News Online environment correspondent
The Royal Society says the Ministry of Defence is jeopardising the development of the UK's renewable energy potential.
The renewable energy target is challenging
The UK's leading scientific body claims the MoD opposes any application to build a wind farm within 46 miles (74 km) of air defence radars.
The only other European country with a limit is Germany which sets it at three miles (5 km), the society says.
The ministry says its opposition is by no means hard and fast, and it often helps developers to choose a good site.
The society says wind energy is expected to make a significant contribution to the government's "ambitious" target of generating 10% of the UK's electricity from renewable sources by 2010.
Realising the potential
But it says figures from the British Wind Energy Association show the MoD objected to 48% of applications to build land-based wind farms last year, and 34% in 2002, because of concerns they could interfere with the radars.
Professor David Wallace, vice-president of the society, has written to the ministry urging greater progress in resolving the problem.
He writes: "My understanding is that the current MoD policy appears to reject any wind development application within 74 km of air defence radars. With 13 such installations, this effective moratorium covers a fairly significant area of the UK.
"Understandably, the MoD has concerns over the effects that wind farms may have on radar in terms of personnel safety, especially for low-flying aircraft and the potential consequences of compromised radars with regard to national security.
Germany's limit is far lower
"It nevertheless concerns me that the restrictions imposed by the MoD are at odds with the rest of Europe, where only Germany imposes a ban, which is set at 5 km."
"Given the technical solutions being developed, how long do you consider it will be before your policies can be brought more into line with our European counterparts?"
Trying to help
The society has also told the Department for Trade and Industry of its concern, and has included it in its submission to the House of Lords science and technology committee's inquiry into the practicalities of developing renewable energy.
An MoD spokesman told BBC News Online: "We can't have a wind farm within 74 km of an air defence radar installation when it's in the direct line of sight.
"But it does depend very much on the topography. Where you have any natural or artificial feature in the way - a hill, say, or a city with tower blocks - then there's no problem.
"We objected to fewer than five applications in 2003. Normally companies suggest up to six or seven possible sites in any application, and we say which would cause us problems and which would not."