The London Assembly has a longstanding opposition to Heathrow expansion for a very clear reason. We don’t need it and we don’t want it.

Last May, the Assembly called upon the Airports Commission to reject both of the Heathrow expansion options. Mayor Boris Johnson added, in a response to a written question in June: “My team and I concluded that the Commission’s assessment had failed to demonstrate that Heathrow expansion could be compatible with the UK’s air quality obligations under EU law. It is simply inconceivable that Heathrow expansion could be allowed to proceed in these circumstances.”

So, the position of the mayor and the London Assembly is completely clear. A third runway at Heathrow would undermine efforts to tackle air pollution and climate change, and increase noise for millions of Londoners.

We know that Transport for London (TfL) and the Greater London Authority could help fund a legal challenge by London borough councils’ to this decision. To us, the pro Heathrow supporters are out of touch and are in the pockets of big business.

According to the Davis report, around 30 percent of new Heathrow passengers are simply people who would otherwise fly out of another London airport. So that’ll be concentrating air pollution in one place. Can that be sensible?

How many London residents, school children and businesses will experience worsening or illegal levels of nitrogen dioxide or particulate exposure? Why are we considering taking 10m passengers a year from other London airports and concentrating them all at one of most polluted hot spots in the country?

It’s predicted that Heathrow will be breaching European legal pollution limits in 2030, when still running under capacity. It will be much higher when at full capacity. TfL also think the Davis Report underestimated the pollution from surface access.

So why make it impossible to meet air quality laws, just to get 10m passengers flying out of Heathrow instead of Gatwick or Stansted?

So hundreds of thousands more Londoners will have to put up with aircraft noise, just so people can stop off in Heathrow’s duty free

The government is signed up to targets on carbon emissions. To meet them, its latest modelling shows it would need to impose a carbon tax on fuel adding £100 to the cost of a return flight to Ibiza by 2050, even if there is no airport expansion. One of the initial reports by the Davies Commission published a graph showing that, to meet those targets after expanding airport capacity, that additional cost would have to be around £150.

In other words, we’d build a new runway in a London airport – then tax people so no more flights were taken across the UK as a whole. If Department for Transport modelling is accepted, it implies a massive switch of flights away from Scottish and regional airports as the South East airports grow.

Who benefits from this growth? Around 5 in 10 new passengers will just be transferring between international flights. So hundreds of thousands more Londoners will have to put up with aircraft noise, just so people can stop off in Heathrow’s duty free.

This expansion would mean spending at least £18bn on a third runway, creating all these problems, not to mention the climate impacts, even though only 10 percent of flights is actually a new connection for British passengers. Why create so many problems when we could easily get the extra passenger journeys out of existing capacity at other British airports?

When we also consider that business flights are falling – and that most of the increase is due to relatively wealthy people choosing to take even more flights each year – the idea of expanding airport capacity looks a nonsense. It’s not even big business, as such, but rich businessmen pushing for it.

Darren Johnson represents the Green party in the London Assembly.