Conservatives in turmoil as ministers hit out over Heathrow runway decision

Transport Secretary Chris Grayling said the decision was the "right thing for the whole country", but accepted that it would be hard for those living near to the airport.

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"Of course it is difficult if you're directly affected by the change - and I feel deeply sorry for those who are - but ultimately in politics you have to do what's best for the whole United Kingdom, and if we're going to create a country that works for everyone in it then this is the kind of thing we're going to have to do to make a difference for the future," he told Sky News.

Conservative bosses were forced to announce the party would not fight the by-election triggered by Zac Goldsmith in protest over the third runway.

The Richmond Park and North Kingston constituency was held by the Liberal Democrats until 2010 and splitting the Tory vote could allow them to retake the seat.

Mr Goldsmith said the decision to push ahead with the new runway was "catastrophic" and announced he will stand as an independent.

The high profile environmentalist insisted the fight to stop expansion was not over, and said the by-election would be a "chance to send a message to government".

Mr Goldsmith said the Government had chosen the "most polluting, most disruptive, most expensive option", but it had "also chosen the option with the least chance of being delivered".

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"The sheer complexity, cost and legal difficulties mean it is unlikely ever to happen," he said. "It will be a millstone round this Government's neck for years."

Mr Grayling said he was "sorry" about Mr Goldsmith's decision, adding: "I wish he hadn't taken this decision, but the reality is you can only deal with the world as it is rather than how you would like it to be."

The Transport Secretary earlier told the BBC Radio 4 Today programme that the Heathrow runway might be built over the M25, saying it would be "cheaper and quicker" than tunnelling under the road.

"I am, of course, very concerned to make sure that, as this runway is built, it doesn't cause massive disruption on the M25, so I think this is a sensible way.

"It is a very gentle hill up which the planes would take off rather than a flat surface. It's what happens at very many airports around the world."

The Government backed a third runway after rejecting proposals to expand an existing runway at Heathrow or build a second runway at Gatwick.

A public consultation will now be held on the impact of expansion at the west London hub before the final decision is put to MPs for a vote in the winter of 2017/18. A new runway could be operational by 2025.

The Prime Minister moved to head off possible Cabinet resignations by giving ministers freedom to speak out against the decision.

That allowed Mr Johnson, along with Education Secretary Justine Greening, to make their opposition explicitly clear.

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Ms Greening said she was "extremely disappointed", while Mr Johnson said there were "colossal" problems with the proposal and anticipated it would be "snarled up" in legal cases.

"I think it very likely it will be stopped," he added.

Windsor and Maidenhead Council, which is in the Prime Minister's constituency, along with Hillingdon, Richmond and Wandsworth local authorities put the Government on notice in March that they would go to the courts if a third runway was approved.

But Mr Grayling ruled out any rethink on the Government's support for the new runway.

He told MPs on Tuesday: "It's very important to say that the Government has decided very clearly today on its recommendation.

"That recommendation has to be validated in a statutory process, it has to be voted on and confirmed by this House, that is what will happen.

"But we're not entering this process with a view to changing our mind."