Boris Johnson's dream of constructing a major new airport in the Thames Estuary received a boost today, after David Cameron said the government would examine its feasibility as part of a wider aviation strategy.

Plans for a third runway at Heathrow in West London were shelved by the coalition when it came to power.

But speaking at Institution of Civil Engineers in London on Monday, the prime minister said he was "not blind to the need to increase airport capacity, particularly in the south-east".

"We are acting now to make the best use of existing capacity. Gatwick is emerging as a business airport for London, under a new owner competing with Heathrow," he said.

"But we need to retain our status as a key global hub for air travel. Not just a feeder route to bigger airports elsewhere, in Frankfurt, Amsterdam or Dubai.

"Yes, this will be controversial. We will need to take decisions for the long-term – and we will be bringing forward options in our aviation strategy which will include an examination of the pros and cons of a new airport in the Thames estuary."

Cameron's speech comes as Johnson gears up to take on Ken Livingstone to remain Mayor of London.

Transport secretary Justine Greening was a key campaigner against the expansion of Heathrow while in opposition but now has the job of managing the future of aviation in the Britain.

"The challenge is making sure we don’t just stay well-connected with markets in North America, Europe and more traditional economies we’ve traded with," she told Total Politics magazine.

"We’ve got to make we stay connected with new economies, new investment and new business and that’s the challenge. How can we make sure we make the best out of the capacity we have for aviation? They’re not easy questions to answer."

She added in an interview due to be published on Tuesday: "Alongside the draft aviation strategy, we will kick off a broader piece of work, looking at our hub airport status and how we can maintain that in the medium and long-term of our country."

Plans to build a new airport to the east of London faces stiff opposition from local MPs. Tory MP Tracy Crouch has slammed proposals for a so-called 'Boris Island' airport as a "tedious, unnecessary, expensive waste of taxpayer money".

The plans are also opposed by deputy prime minister Nick Clegg who has said he is "unpersuaded" of the need to build a new airport.

Speaking in January he said: "I'm totally un-persuaded by the evidence and think we should take a common-sense, hard-headed look at the facts. I don't think we should as a country decide to concrete over vast swathes of the Thames Estuary on a whim."