Government plans for a massive expansion of the UK's offshore wind farms are facing fresh challenges after reports emerged claiming the Ministry of Defence (MoD) is hardening its opposition to the proposals amidst concerns wind turbines are causing serious interference to radar systems.

A report in The Times claims that the MoD has lodged "last minute" objections to at least four onshore wind farms on the east coast because they jeopardise its ability to spot aircraft.

The paper adds that the department is likely to voice similar objections to proposed wind farms in the North Sea, announced by business secretary John Hutton last month, as they would be directly in line with three radar stations on the Northumberland, Yorkshire and Norfolk coasts.

Trials carried out in 2004 and 2005 revealed that wind farms could cause severe disruption to radar systems. Giving evidence to a planning inquiry last year Squadron Leader Chris Breedon wrote that interference to radar signals above and around wind farms occurred "regardless of the height of the aircraft, of the radar and of the turbine".

In a statement on its website the MoD insisted it was not pursuing a policy of blanket opposition to wind farms near radar stations. "All wind farm applications are assessed on a site by site basis," it said. "The MoD is committed to Government targets for renewable energy and whenever possible we seek to work with wind farm developers to find a mutually acceptable solution."

However, wind industry lobby groups are reportedly furious at the MoD's position and have written a letter to both Hutton and defence secretary Des Browne warning that both millions of pounds of investment and plans to generate 33GW of energy from offshore wind by 2020 could be at risk if the MoD continues to oppose new developments.

The latest revelations comes as the wind industry waits for a final decision on plans for one of the world's largest wind farms on the Hebridean island of Lewis.

Last week reports claimed the Scottish Executive was "minded to refuse" the £500m plans after opposition from locals and wildlife groups. Now developers and local business groups are lobbying the executive in an attempt to save the planned 181 turbine farm, which supporters claim could generate 600MW of energy and revitalise the Western Isle's economy.

Speaking last month, Chris Tomlinson, director of programme strategy at the British Wind Energy Association, warned that the government would fall 1GW short of its target to generate 8GW from wind energy by 2010 unless developments such as the Lewis project are approved. "We need that [1GW of extra capacity] to be consented within the next few months if we are to construct the sites in time," he warned.