In 2010, the government promised no third runway at Heathrow. It was a clear and authoritative statement.

But since then the government’s united front has faltered and their confused direction on aviation has made the airline industry restless.

Powerful chief executives have taken this opportunity to plunge into the debate and throw their weight behind arguments about where expansion is needed to increase capacity in the south east.

We now have a debate dominated by an ‘either, or’ scenario – either a third runway or ‘Boris Island.’ As an advocate of the Estuary Airport, architect Lord Foster has now suggested that the £33bn construction costs will be paid for by a combination of landing charges and the closure and redevelopment of Heathrow.

Meanwhile, the chief executive of the National Air Traffic Service has stated that the Estuary Airport can't co-exist with Heathrow because of a conflict of flight patterns.

No alternative for non-growth has been presented.  

The main driver of this debate has most definitely been the economy and its growth.

We are told London will begin to lose out economically to our competitors if we fail to act now and build new runways.

According to business leaders we need to access the emerging economies of Brazil, Russia, India and China, also known as the BRIC countries, in order to remain a leading global city. But actually I do not believe the economic prosperity of our city hinges on expanding aviation capacity.

The most recent Global Financial Centres Index ranks London as the world’s leading financial centre in terms of competitiveness.

Heathrow has more flights to key business centres than any other European airport, more than Charles de Gaulle and Frankfurt combined.

Only a third of passenger air traffic is important to economic activity in London, with business and inward leisure trips making up just 34% of airport traffic.

Around 100,000 jobs would be lost in West London if a new airport was built in the Thames Estuary, leading to social stagnation.

The £50bn price tag for the new estuary airport is an incredible figure that we simply cannot afford and the airport would not be ready until 2030 at the earliest, clearly not the solution to an ‘urgent’ problem according to business leaders.

But the economy is just one side to the issue - the environment adds a significant dimension to the debate on both sides and has generated healthy opposition. So here are a few practical reasons not to expand our air capacity ...

Expansion at Heathrow would expose 35,000 more people to high levels of nitrogen dioxide and would increase carbon dioxide emissions by 9.8 million tonnes.

Add to this the fact that at least 150,000 more people would be affected by aircraft noise if a third runway were to go ahead, on top of the estimated 725,000 already affected, and it becomes clear why residents living under the Heathrow flight path are opposed to the idea.

Yet these residents are given little consideration and their input is very often ignored completely because the big airline bosses don’t want to and seemingly don’t have to listen.

The coastal wetland that is the Thames Estuary supports a huge variety of wildlife including thousands of migrating birds and their fragile eco-systems. Its importance is recognised by a series of Special Protection Areas which are internationally protected.

Plans for an estuary airport simply do not justify the massive environmental impacts.

There is also a serious threat of bird strike from the 300,000 annual migrating birds that establish themselves each winter the in the estuary. Noise and air pollution from flights operating 24-hours a day would be estimated to affect up to 12 million people who live and work in the Thames Estuary.

The UK is already failing to keep on track to meet EU emission targets. London is one of 40 air quality zones that failed to meet the January 2010 deadline for complying with EU limits for nitrogen dioxide.

Aviation contributes around 37% of total nitrogen dioxid , so increasing the number of runways will increase our emissions and put us even further out of reach of our targets.

I suggest the debate should not be about where expansion is needed, but rather how we manage existing capacity. That's the alternative which has been ignored so far.

Around 100,000 flights from Heathrow are to destinations such as Edinburgh and Paris, which could easily be reached by fast rail alternatives such as the Eurostar.

If we shifted people away from these unnecessary short-haul flights to rail transport, slots would be freed up for long haul flights to the emerging markets.

Transfer passengers make up more than a quarter of passengers at Heathrow, changing from one flight to another. The government would gain more than £500m a year in lost revenue  as transfer passengers do not pay Air Passenger Duty.

New technologies such as video-conferencing could seriously reduce air travel.

Business flying represents a quarter of all UK trips but almost 90% of companies believe video-conferencing can improve their productivity, with 85% saying it could help them to reduce their flying .

Adding capacity at Heathrow or building a new estuary airport would be a step in the wrong direction for the UK.

This should not be the basis of the aviation debate. The government must resist pressure from the airline industry and realise that expansion cannot occur without severe environmental consequences.

The economic case for expansion is also being scrutinised and is now proving weak. But until the government publishes its aviation policy paper, which is already three months overdue, we can only continue to speculate.

Jenny Jones is a Green Party member of the London Assembly

Tags: Aviation policy, Boris island, Heathrow expansion, Thames Estuary Airport