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Does the South-East need more airport capacity?
What are the arguments in favour of expansion?
Heathrow currently runs at close to 100% capacity with demand for air travel predicted to double in the next 25yrs. With this increase in demand, Heathrow arguably will not be able to cope without a third runway.
Heathrow needs extra capacity if it is to reach the levels of service found at competitors elsewhere in Europe in countries such as Germany in the Frankfurt Airport, or it will be overtaken by its rivals.
The third runway will boost the economy by a predicted £7bn a year to the economy, according to airport owner BAA. Some say a third runway is the only solution to the congestion at Heathrow.
Tens of thousands of jobs will be created in construction of the runway in the short term: and for business and in tourism over the longer term.
Lack of expansion at Heathrow would threaten London's position as trading capital of the world, stifling the international links Britain was built on. Business leaders such as Barclays Bank argue London deserves and needs an airport of international quality. The airport said it would be able to cater for 130 million passengers compared to 70 million today, "allowing the UK to compete with our international rivals and providing capacity for the foreseeable future".
Those pushing for the new runway argue that pollution caused by the airport will be closely monitored and kept to low.
By 2020, when the runway would be completed, new technology will mean planes are much quieter and less polluting. The Airbus A380 already demonstrates that planes are moving in this direction and reducing.
It is argued that if the runway were not built, there would be no cut in emissions. Flights would simply move to other European airports. CO2 would not be reduced, merely being emitted elsewhere. This means the pollution concerns are overplayed.
Heathrow argues that a third runway would raise its capacity to 740,000 flights a year, from the current limit of 480,000.

Arguments against expansion
One argument is that we need to reduce, not increase, emissions. Heathrow generates 50% of UK aviation emissions. This makes 6% of total world emissions, according to Department for Transport figures.
There are also a number of negative externalities associated with the expansion plans: Noise and air pollution would increase through expansion. The planes fly over houses on its approach to Heathrow, leading to noise pollution. A third runway could mean an extra 200,000 flights a year over London.
Many of the new passengers that would use the extra runway are unlikely to spend money in London and the economy around Heathrow: according to former BA boss Bob Ayling, “they would spend little or nothing in London, only boosting airline profits.”
To make way for the runway, Sipson - a village of 700 houses - would be demolished and hundreds of acres of greenbelt land would be destroyed.
Alternatives to expansion
However, here are better long-term alternatives. The mayor of London has supported a completely new scheme in the Thames Estuary, which could become a major dedicated hub airport named Boris Island. With growth of internet and tele conferencing, it is possible that business will adapt and limit the growth of business trips rather than expensive travel. For historical reasons, Heathrow is badly located. It is the only major airport with flight paths over a large capital city.
Some, like London Mayor Boris Johnson, believe this is a perfect opportunity to start again and propose a new airport in the Thames Estuary, while completely removing the Heathrow site because of the negative externalities associated with it. Planes would approach and leave over water, reducing the impact of noise and the airport could operate 24 hours a day, meaning the possible number of flights leaving and entering would be less limited than if the airport were over land.