GIANT wind turbines the size of London's Big Ben clock tower are coming to County Durham.

The four windmills, standing at 100 metres tall, will be the biggest and most powerful to be built on the UK mainland.

They will be built on two remote rural sites.

Two turbines will go at Holmside Hall Farm, which is 100 yards from Craghead, near Stanley. The second pair will go at Crowshouse Moor, south of Harehill Farm, Haswell, near Durham.

They will provide enough electricity to power 4,500 homes, reducing carbon emissions by 9,000 tonnes a year.

The investment, by energy company Powergen Renewables, is part of the Government's environmental drive to generate more power from renewable sources such as wind, water and wood.

The company said it hoped to start work at Holmside and Harehill in late summer or early autumn, with the turbines to be generating electricity by early next year.

A spokeswoman said: "These 2.75 megawatt turbines will stand around 100m to tip height, roughly the same height as Big Ben, and will be the biggest and most powerful on the UK mainland so far.

"They have been designed to have as little impact on the environment as possible and will be painted in muted colours to blend in with the background.

"They are very big, but some people think wind turbines are quite nice to look at and they often become something of a tourist attraction."

Durham City Council and Derwentside District Council granted planning permission for the two sites in 2000, with very little local opposition.

The turbines are part of a £120m programme to boost renewable energy production.

Powergen has also signed an option for lease for a wood-burning power station at Lockerbie in Scotland, an off-shore wind farm off the coast of Great Yarmouth and hydro power stations at Rannoch in Perth and Kinross and Garbat in the Scottish Highlands.

The company already has 16 wind farms, producing enough power to supply 82,000 homes. The new projects aim to increase the company's renewable capacity by 1,000megawatts by 2010.