David Cameron has officially opened the world's largest operational offshore wind farm - London Array.

The Prime Minister toured the site by helicopter on Thursday, and declared it a 'huge privilege' to be in Margate for the opening.

He congratulated everyone who had been involved in the scheme, which was "great for Kent and great for Britain".

As many as 141 of 175 3.6MW Siemens turbines are now able to generate 507MW of energy for UK homes and businesses.

They can now supply enough green electricity to power half a million homes - equivalent to two-thirds of Kent.

London Array - 12 miles off the Thanet coast - generated its first power last October, feeding renewable energy to an onshore site at Graveney, and then into the National Grid.

The final turbine was installed in December last year and the project is expected to be fully operational in Spring.

The first phase is costing £1.76bn.

Speaking at the opening, RenewableUK’s Chief Executive, Maria McCaffery, said: “The Prime Minister’s ringing endorsement of Britain’s offshore wind industry is a real boost for the entire renewable energy sector, which is a key growth area for the British economy.

"London Array is a magnificent feat of green engineering in a field in which Britain is the global leader, as we have more offshore wind capacity installed than the rest of the world put together.

“We’re about to witness a massive expansion in the number of people we employ in the windindustry onshore and offshore, from about 12,000 now to 76,000 by the dawn of the next decade, as long as Government remains supportive – today Mr Cameron has assured us that it will”.

Earlier, campaigners against government austerity measures were protesting outside the Turner Contemporary ahead of the visit.

David Cameron visited the Margate gallery amid feverish speculation of the visit on social networking sites.

Campaigners were outside the seafront building making their voices heard against cuts in benefits and public services.

Video: David Cameron visits the London Array windfarm - as protesters wave placards