Airport expansion: What happens next?

After nearly three years of deliberation the Davies Commission on airport expansion has given its opinion. So what happens now?

Out of three possible choices on the table, Howard Davies' team has backed the idea of building a new third runway at Heathrow.

The plan involves building a new 3,500m runway about two miles north of the two runways Heathrow already has at an estimated cost of £18.6bn. The Commission said the idea of extending one of Heathrow's existing runways was less advantageous.

Heathrow is one of the world's busiest, handling 70 million passengers in 2012. More than a third transfer to other flights, making it a major hub airport. But it operates at 98% of its capacity - much closer to capacity than other major London airports and rival hubs in Europe.

Heathrow said in its submission to the Commission that extra capacity would be delivered between 2025 and 2029.

In a nutshell: the Heathrow scheme is predicted to create the most jobs and make the most money for the country.

Heathrow expansion is seen as the best short-term option to keep Britain competitive with its European rivals, like Amsterdam Schiphol and Paris Charles de Gaulle. Heathrow is a big employer and supporters cite a knock-on effect on businesses in the area.

Sir Howard Davies's report says that the new runway should come with severe restrictions to reduce the environmental and noise effects.

Night flights should be banned and the government should make a Parliamentary pledge not to build a fourth runway.

The report also recommends an aviation noise levy to fund insulation for homes and schools and says a legal commitment should be made on air quality.

The environmental impact. Susan Pearson, of the Airport Watch campaign, says Heathrow would become the biggest emitter of carbon dioxide (CO2) in the country.

The airport has argued that it is near two of Britain's busiest motorways - the M25 and M4 - and most local pollution is caused by vehicles rather than aircraft engines.

Noise pollution would become even worse for the 760,000 people already living under the flight path - and some homes would have to be demolished.

The money to build the new runway will be raised privately, but we all pick up some of the tab for additional infrastructure.

Bigger airports mean more passengers, and they've all got to get there on wider roads and better train services.

It is expected that expanding Heathrow will entail putting part of the M25 in a tunnel. Overall it is estimated the Heathrow scheme would cost taxpayers £5.7bn.

Then there are fares. To pay for all the work, Heathrow will charge the airlines more to land. And airlines may pass on some of that extra expense to passengers. However, Sir Howard Davies argues that extra competition should eventually lead to lower ticket prices.

An expansion of Gatwick was also on the table at a cost of £9.3bn. And the second Heathrow option: doubling the length of one of the existing runways at a cost of £13.5bn.

The Gatwick proposal would have involved building a new runway, at least 3,000m long, built far enough away from the existing runway to allow for fully independent operation.

Gatwick is the world's busiest single-runway airport, but only 5% of passengers transfer to other flights.

Gatwick argued that adding a second runway there would have involved fewer people being affected by noise and pollution than the number affected by a third runway at Heathrow, which is closer to central London. Gatwick already has good transport links to London.

Mayor of London Boris Johnson has long championed a new four-runway airport in the Thames estuary to replace Heathrow, but the Commission has rejected the idea.

A plan to open up RAF Northolt - about six miles from Heathrow - for short-haul civilian flights was also rejected.

The Commission last year decided not to shortlist proposals for expanding Stansted or Birmingham, but said they could be considered as "potential options" for any second new runway by 2050.

There's a long way to go yet. The Davies decision is just a recommendation.

It's thought ministers will then need to run their own consultation, just a short one, maybe a few weeks, to hedge against legal challenges.

George Osborne has in the past hinted that he wants to get on with it as soon as possible, but even if the politicians race it through as quickly as they can - and there is likely to be plenty of political opposition - there may be legal challenges and planning permission to deal with and new infrastructure to build.

No new runway will be open for at least another decade.

Transport Secretary Patrick McLoughlin has said the UK needs to increase its aviation hub capacity to compete with international rivals. That view is shared by some politicians and business leaders, but others argue that no credible case has been made.

Friends Of The Earth campaigner Jenny Bates says: "The overall business case for further expansion of our airports is just not convincing, as it is not compatible with meeting our climate change targets."

Airport Watch, a group opposed to airport expansion that might harm the environment, has said more effort should be made to utilise existing capacity.

And the Aviation Environment Federation has said the idea the UK is facing an airport capacity crisis is a myth.