Renewable energy sources must be “financially sustainable” if they are to meet the world’s needs, the Prime Minister David Cameron has said.

The level of private investment in wind power is encouraging, say ministers.

A meeting of international Ministers was held last week when Mr Cameron welcomed the investment of £350 million to create 800 jobs in the energy sector, but he says the main challenge is to drive down costs.

Mr Cameron said at the event opening that “a more diverse, cleaner mix of energy sources that will give us… security without causing irreparable damage to the planet”.

He added: “Renewables are now the fastest growing energy source on the planet. And I am proud that Britain has played a leading role at the forefront of this… revolution”.

The Conservatives pledged to lead “The greenest government ever” but this is being hailed as an unfulfilled promise by many environmental groups.

Andy Atkins of Friends of the Earth said “In the very week we find the UK back in recession there is more need than ever to build a clean economy, and create the thousands of jobs this would bring. “With soaring gas costs sending household fuel bills rocketing, David Cameron should be championing clean British energy and leading the drive for a low-carbon future, not dodging the chance to advance this on the world stage.”

The Prime Minister had previously stressed the need for governments and businesses around the world to work together to lower the cost of renewable energy and develop a global carbon price.

He said that between April 2011 and February 2012 investments worth £4.7 billion have been announced in UK renewable energy and its supply chain, supporting or creating 15,000 jobs.