Airport capacity is a divisive issue in Britain, pitting popular London Mayor Boris Johnson against Prime Minister David Cameron at a time when the British leader is facing a damaging rebellion from inside his own ruling Conservative party.

Cameron's government is facing increasing demands for an acceleration of infrastructure projects as it seeks to breathe new life into the economy.

Business leaders say more airport capacity is crucial to boosting trade and routes to developing markets as competition heats up from more attractive hubs in continental Europe.

Johnson, a Conservative tipped in some quarters as a possible future prime minister, said the government was dragging its feet over aviation and losing momentum against other more aggressive market players.

"It is a policy of utter inertia," Johnson told BBC Radio.

"Can I tell you in the next nine years how many runways they are going to build in China? They are going to build 52. How many are we going to build in the UK? None at all."

He said an inquiry on the aviation sector's future, launched on Friday and due to report after the next general election in 2015, was taking too much time.

"I think what is going on now is a good thing, it's a productive process. I just think it could be speeded up, and there is absolutely no need to delay to 2015."

Heathrow is the world's third-busiest airport but it is close to full capacity. The government needs to decide whether to expand its existing facilities or consider other options.

The Conservative-led coalition blocked construction of a third runway there after it came to power in 2010. The idea of another runway had been unpopular with local voters and green groups as it would have meant a huge increase in the number of planes flying over London and its densely populated suburbs.

But speculation has been growing that Cameron could still go back to the plan if he wins the 2015 election.

Riding a wave of popularity following London's widely praised Olympic Games, Johnson is campaigning for a brand-new new airport in the Thames Estuary - a lavish project widely known as "Boris Island".

He has demanded Cameron rule out the Heathrow third runway option both during the current parliament and beyond, a call echoed by other Conservatives in areas under its flight path.

The aviation inquiry, chaired by former Financial Services Authority head Howard Davies, says it would review all expansion options fairly and come up with an interim report next year.

Options on the table include expanding existing airports such as Heathrow, Gatwick and Stansted, connecting London by high speed rail to an airport in the city of Birmingham as well as building Boris Island.

Davies denied his mission was part of a government ploy to kick the tricky question "into the long grass" for political reasons.

"Some of the criticism assumes that we will go into a huddle for a couple of years and then come out with 'X solution'. It's not going to be like that," he told reporters.

"I do take the view, perhaps a naive view, that political opinions do to some extent reflect the fact that there are difficult choices here." (Editing by Mark Heinrich)

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