Theresa May has insisted a third runway at Heathrow Airport will meet the required air quality standards.
Responding to concerns raised at Prime Minister's Questions by Tania Matthias, the Tory MP for Twickenham, Mrs May said: "The government looked very closely at this issue of air quality and environmental impact of all three schemes that were proposed by the Airports Commission. We took extra time to look at those. We wanted to look more particularly at the air quality issues.
"The evidence shows that air quality standards can be met as required by all three of the schemes including the north west runway at Heathrow.
"But... the issue is about more than airports, because the question of air quality is also about road transport and that's why we are looking to do more in relation to what we're doing for air quality. It's why, for example I'm pleased to see that we're at such a leading edge in the provision of electric vehicles."
Tory MPs are taking lumps out of each other on Heathrow, grammar schools and - above all - the true meaning of Brexit.
Environmentalist Goldsmith called the move "catastrophic" - and announced he will now stand as an independent in protest.
The expansion of the London airport will affect the whole of the UK, with more domestic routes, while impacting air fares and house prices.