In the run-up to the GLA elections last year the London Assembly and its members across all the political parties adopted a resolution against the further expansion of Heathrow – a policy also supported by all the major mayoral candidates.

Since being re-elected to the London Assembly, I have been appointed as the Assembly’s representative on the Heathrow Airport Consultative Committee (HACC), where I have argued that we do not want a bigger Heathrow but a better one, particularly with regard to surface transport options for the users of the airport.

With the Government’s announcement on the proposed third runway at Heathrow airport imminent, it is useful to take stock of the position of the London Assembly on this issue and outline the arguments on which we base our stand.

In February 2008 the London Assembly Environment Committee, of which I am now deputy chair, submitted a formal response to the Department for Transport (DfT) consultation on Heathrow, objecting to expansion on the grounds of its impact on economic development, climate change, noise pollution and air quality. The Environment Committee remains unconvinced that the expansion of Heathrow is essential to the well being of the London and wider UK economy, or that the conditions placed on expansion by the government have adequately addressed the environmental costs and impacts of a third runway.

With regard to economic development we have taken the view that the DfT has not adequately considered the trends in passenger behaviour and the resulting growth of other airports serving London. Since 1990 the number of destinations from Heathrow has declined by 20 per cent but Gatwick for example now serves 20 more destinations than Heathrow. Between 2000 and 2006 passenger numbers increased by only 5% at Heathrow but by 18% in London airports overall. So while Heathrow’s capacity has been contained, until recently London’s financial sector has thrived. In failing to take account of these developments, the DfT has overestimated the importance of Heathrow to the London and UK economy.

On the issue of climate change it is difficult to see how the government’s new target of an 80 per cent reduction by 2050 in CO2 emissions can be achieved if the construction of a third runway at Heathrow is allowed. So it is for good reason that campaigners see the battle to stop expansion at Heathrow as the “iconic fight against climate change in the UK”. At the very least, expansion should not be considered till the Kyoto agreement includes aviation emissions as part of its binding criteria and the EU carbon emissions trading scheme has demonstrated its effectiveness in reducing UK and European emissions.

For Londoners, particularly in the west, the local environmental issues – noise pollution and air quality – are the most pressing issues.

On the noise front, it is quite clear that the 1986 Airport Act is inadequate and needs to be reformed or replaced with a more robust mechanism to enforce stringent environmental standards on noise levels. The conditional noise contour parameter should be increased to 50 decibels and effective measures introduced to encourage the adoption of quieter, cleaner engines.

As for air quality, the London Assembly has called on the DfT to give a guarantee that it will not seek an exemption for areas around Heathrow in implementing EU air quality standards in 2010. Before expansion should be considered vast improvements are required on surface and ground transport accessing the airport, as this is the biggest single factor causing the decline in air quality.

With the gloves soon off in the campaign against Heathrow’s extra runway, we can expect a package of transport measures to ease ministerial and backbench unease, such as a high-speed link with the North being built before a new runway is constructed, as part of a package to make Heathrow expansion acceptable.

I am confident that the climate change debate and European law will ensure that the third runway is never built. As already noted, Heathrow expansion on its own would scupper any government targets to cut CO2 emissions. In the meantime, Londoners will continue to switch their use of airports from Heathrow to others in Greater London.