"Where we are testing planes we need to minimise the risk to aircraft and personnel," the spokesman told Reuters.

The government sees offshore wind power as a key part of its strategy to boost the use of green energy and the MOD objections will threaten its target of generating 10 percent of Britain's electricity from renewable sources by 2010.

The MOD wants to block offshore sites in the Irish Sea at Southport, where a scheme has been put forward by German wind energy developer EnergieKontor, and at Shell Flat which is home to three schemes.

The developers at Shell Flat include Danish energy company Elsam, Royal Dutch/Shell and CeltPower, a joint venture between Scottish Power and Japanese trading consortium Tomen Corp.

"These sites are near Warton where British Aerospace undertakes aircraft training for the RAF (Royal Air Force)," said the MOD spokesman.

In addition, the MOD is in talks with London Electricity and Germany's Enertrag as it is unhappy about their plans for a wind power site off Cromer in Norfolk, in eastern England.

BLADES COULD INTERFERE WITH RADAR

The MOD's main concern is that the whirring blades on the towers, which can be over 100 metres high, could show up on radar systems and look like moving aircraft.

Shell says it has carried out studies of the effect on radar and believes any impact can be managed by existing systems.

"The wind farm is not in the line of approach of any runway. Blackpool airport which is closer to the farm than Warton has not anticipated any problem," the Shell spokesman said, adding the company was in talks with the MOD on the issue.

Only one offshore wind scheme is operating in Britain, at Blyth off England's north east coast, but the government wants to expand the offshore wind sector so that it provides 1.8 percent of Britain's energy needs by 2010.

Britain has installed about 400 megawatts of wind generating capacity, almost all of it onshore. This is only a fraction of Germany's total capacity of 6,900 megawatts.

In countries like Germany, Spain and Denmark wind power has been developed without compromising defence systems, say UK wind power companies.

The Department of Trade and Industry has set up a working group on the radar issue which includes officials from British Wind Energy Association (BWEA), which represents wind power developers, and from the military.

"The idea is to get some movement in the current impasse. We need to bring some clarity to the issue," said Chris Shears, BWEA board member responsible for radar issues.

The group has commissioned three reports and hopes to issue guidelines on the radar problem within a year, he said.

The MOD is also trying to block the huge 80 MW onshore Kielder wind farm in northern England on radar grounds.