Tory MP Zac Goldsmith has quit after the Government said it would push ahead with what he called a "catastrophic" expansion of Heathrow Airport.
The Richmond Park MP had already made a public pledge to resign and stand as an independent candidate in his seat if the decision was taken.
After expansion was confirmed by the Cabinet, Mr Goldsmith took to Twitter to say: "Following the Government's catastrophic Heathrow announcement, I will be meeting my constituents later today before making a statement."
It then emerged that Mr Goldsmith had already contacted his local party association to confirm his intention to fulfil his promise.
Tory MP Tania Mathais, whose Twickenham seat is also one of the most affected, said on Twitter: "Terrible decision by Govt. I will continue to fight against 3rd runway at Heathrow. I am confident there will never be expansion at Heathrow."
James Berry, the Tory MP for Kingston and Surbiton, said: "Just heard Heathrow has been chosen over Gatwick. I'm very disappointed."
Theresa May, who already has only a small majority in the Commons, now faces a potentially difficult by-election and losing one Tory seat in South West London.
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