Government promises to speed up planning inquiries to ensure that wind farms play a valuable role in providing clean energy are not being fulfilled, with many schemes waiting up to five years for the go-ahead. Ministers have pledged to remove or reduce barriers faced by companies that want to build sustainable power projects, but this is proving difficult.

The development of E.ON's Humber Gateway project is one of the schemes mired in difficulties and facing ever-increasing delays. "When built, this wind farm will be one of the biggest in the UK and will play a vital role in the fight against climate change," said E.ON's project manager, Chris Sherrington. But the planning authorities are stuck, debating the effects on shipping routes despite the site having being chosen specifically to avoid interference with shipping and having full support from ABP, which owns Humber ports.

The fragility of the wind power business was highlighted recently when Shell pulled out of the world's biggest offshore wind farm - the London Array, off Kent - because of spiralling costs associated with planning delays. Britain is already struggling to meet the EU target of producing 20% of the country's total energy from renewables by 2020. That target has been reduced to 15% but even that is a major leap given the current level of 2% - a figure that has not risen for several years.

The Clyde Wind Farm in Scotland, being developed by Airtricity, is also suffering at the hands of the planning authorities. The project is more than five years behind schedule, with the planning application made in February 2003 and the referral from local planning authorities to public inquiry not occurring until August 2006. Airtricity, now part of Scottish and Southern Energy, says it remains hopeful that "a decision is imminent".

Planning for Gwynt-y-Môr wind farm situated 16km off the coast of north Wales, was proposed by npower in November 2005. The project, capable of generating up to 750MW or enough to power almost half of the households in Wales, is still awaiting a decision from planning authorities despite the fact that it would prevent the release of approximately 2m tonnes of carbon dioxide into the atmosphere.

The average time for planners to reach a decision has increased to more than 24 months in the past four years and delays often depend on the part of the country in which the scheme is being developed. E.ON estimates that, on average, a project spends between two to three times longer in the Scottish planning system than in the English one.

New figures from the British Wind Energy Association's annual review show that approval rates in Northern Ireland and Wales averaged 93% and 77% respectively last year, in comparison with England's and Scotland's rates of 65% and 56%.

The statistics show that there are 172 wind farms with 2,500MW of power in operation. This is enough to provide energy for 1.4m homes. There are 35 more wind farms with a capacity of 1,400MW under construction and 222 in the planning stage that could provide 9,200MW.

Gordon Brown promised to speed up planning delays in a speech on climate change in November last year. "The government will do more to remove the planning and other obstacles that are currently holding renewables back," he said. "I have asked the secretaries of state for defence, business and transport to ... identify and test ... solutions to the potential difficulties wind farms pose to air traffic and defence radar."

However, the government's initiative to speed up the planning process could be starting to have an effect. Ian Marchant, chief executive of Scottish and Southern Electricity, commenting on approval for a project lost in the planning system until recently said: "Gordonbush is the fifth SSE wind farm to receive consent in the last 18 months or so. While the Gordonbush proposal has spent almost five years in the planning system, there are encouraging signs that the planning process is beginning to speed up.

"Given the scale of the energy challenges facing the country, it is important these encouraging signs represent a sustained commitment to a better planning process," he said.