Two of the world's leading wind farm operators have teamed up to make joint bids for the next round of offshore licences in Britain.

ScottishPower Renewables, part of Spain's Iberdrola Renovables, is joining forces with Sweden's Vattenfall with the aim of developing 6,000 megawatts of installed capacity.

The partners have not said how much the development will cost, but industry experts believe the investment will run into several billions of pounds. The partnership will take the form of a consortium which will submit its tender to the Crown Estate under the third round of licences for offshore development.

"Round three is a very important part of the UK's renewable aspirations and this consortium has the skills and determination to play a key role in this process," said Xabier Viteri, chief executive of Iberdrola Renovables.

Both Iberdrola and Vattenfall already have significant wind farm operations. Within Iberdrola, ScottishPower operates 550 megawatts of capacity across the UK and Ireland. It is also building what it describes as the world's largest onshore windfarm at Whitelee, south of Glasgow, and has received consent for its first offshore windfarm off the Cumbria coast, west of Duddon Sands.

Vattenfall owns two of the world's largest offshore windfarms, Lillgrund off the south coast of Sweden and Horns Rev in the Danish North Sea. In the UK it owns Kentish Flats in the Thames estuary and recently bought Amec Wind Energy and Eclipse Energy.

Yesterday, as well as the partnership with ScottishPower, the Swedish company said it had bought the Thanet Offshore project. It paid £35m for the scheme, which will have an installed capacity of 300MW. The investment required will be about £780m.

Anders Dahl, the head of Vattenfall's wind power division, said: "Great Britain is ideal for wind power with good wind conditions and a long coastline."

Mike O'Brien, energy and climate change minister, said: "I am pleased Thanet windfarm will be able to proceed under its new owner, Vattenfall. This proves the UK is still a good place to invest in offshore wind despite the current economic difficulties. The UK is a world leader in this technology. Our plans for more windfarms offshore will not only help in the fight against climate change but will increase the amount of home grown energy and create jobs."

Rob Hastings, director of the marine estate at The Crown Estate, said: "We are very pleased that Vattenfall have completed this deal to buy Thanet. The UK is now the world's leading producer of offshore wind power and we will be working closely with Vattenfall to ensure the build schedule is maintained."

Last year the then business and enterprise secretary, John Hutton, indicated Britain could build up to 33 gigawatts of offshore capacity by 2020.