Theresa May faces a tough fight to secure a third runway at Heathrow

A by-election, Cabinet dissent, legal challenges – including one from the Prime Minister’s local authority – all threaten the decision

Expansion of the west London airport has divided Tories, with Zac Goldsmith resigning, and Boris Johnson describing the runway as 'undeliverable' (Getty)

Theresa May faces a daunting fight on several fronts to secure a third runway at Heathrow after the long-awaited go-ahead sparked a Tory civil war today.

Business groups and trade unions reacted with delight to what one cabinet minister called the “truly momentous” decision to expand Heathrow, after decades of dithering and delay.

But Zac Goldsmith, the defeated Conservative candidate for London Mayor, told his local party he would resign and refight his nearby Richmond Park seat – branding the decision “catastrophic”.

The Conservatives said they "disagreed" with Mr Goldsmith, but announced they would not run a candidate against him.

The move will also give the Liberal Democrats a by-election opportunity in a pro-EU seat that overwhelmingly voted Remain.

Boris Johnson – given “special dispensation” by Theresa May to speak out for a limited period – made clear his continued opposition to expansion, predicting it “will be stopped”.

However, the Foreign Secretary did not repeat his celebrated pledge to protestors to “lie down with you in front of those bulldozers and stop the building, stop the construction of that third runway”.

Instead, he suggested the proposal would be "snarled up" in legal cases, insisting: “The day when the bulldozers appear is a long way off, if indeed they ever materialise.”

The legal challenge is planned by four Conservative-run local authorities, who have already instructed lawyers to prepare a case in alliance with Greenpeace.

Significantly, the group worked together in 2010 to win a High Court battle over the plans by Gordon Brown’s government to expand the west London hub.

Furthermore, to the discomfort of the Prime Minister, one of the four is her local council of Windsor and Maidenhead – whose cause she used to support.

Opponents of expansion dug out a 2009 statement in which Ms May warned that many of her constituents in Maidenhead would be “devastated” by the go-ahead for a third runway.

The pages on Ms May's website – which now appear to have been deleted – included a statement from herself, declaring: “I am clear that we must say no to a third runway at Heathrow.”

Asked what had changed, the Prime Minister’s spokeswoman said she was backing a bigger Heathrow in “the national interest”, saying: “This is not a decision about a constituency.”

Friends of the Earth condemned the planned expansion, saying: “Local communities now face more noise, more air pollution and more misery from a quarter of a million extra flights each year.”

And Jonathan Bartley, co-leader of the Green Party, said the decision “puts a wrecking ball through the Government’s claim to be concerned about climate change”.

But Paul Drechsler, president of the Confederation of British Industry, led business groups in welcoming “an enormous relief to firms in every corner of the country”.

He added: “It will create the air links that will do so much to drive jobs and unlock growth across the UK, allowing even more of our innovative, ambitious and internationally focussed firms, from Bristol to Belfast, to take off and break into new markets.”

And the British Chambers of Commerce said: “Building this runway will not only boost business confidence, it will also help firms access export opportunities, and attract investment from both UK and overseas businesses.”

The Government hopes to bring down the curtain on almost 50 years of airport indecision by backing the third runway, which will not open fully until 2030 at the earliest.

The move will end, at least temporarily, Gatwick’s bid for a second runway, in a move that could also trigger a High Court challenge.

Heathrow expansion will be dependent on a ban on night flights, a legal block on any fourth runway, guarantees on the expansion of domestic flights and more passengers using public transport, to cut pollution.

The Government will also urge Heathrow to cut the cost of the £17.6bn scheme, much of which will fall on taxpayers for huge transport improvements around the airport.

Today Transport Secretary Chris Grayling repeatedly refused to say what the Government’s bill might be for work likely to involve moving the M25 motorway.

The expansion plan could also run into opposition from Heathrow’s biggest airlines, which fear the massive cost of the third runway will price out passengers.

Both British Airways and Virgin Atlantic warned that landing charges are already the highest in the world, insisting a further hike is “not an option”.

It raises the possibility of major airlines pulling out of a three-runway Heathrow and expanding elsewhere unless the airport guarantees to cap passenger fees.

As well as a looming by-election, the Prime Minister has yet to decide how to manage the split in her Cabinet, other than to allow Mr Johnson and Education Secretary Justine Greening to oppose expansion – for now.

She has yet to say whether Conservative MPs will be granted the extraordinary licence of a free vote when the decision reaches the Commons next year.