Controversial plans for a third runway at Heathrow Airport have been approved by ministers after years of argument and delay.

The government's economic sub-committee, chaired by Prime Minister Theresa May, backed the plans which were then approved by her full cabinet.

MPs will be asked to decide on the expansion plans in the coming weeks.

Transport Secretary Chris Grayling said it was a move taken in the "national interest" and based on the evidence.

He told MPs it was a "historic moment" which would boost the UK economy and create thousands of jobs.

But former Conservative transport secretary Justine Greening said the plans were "ill-conceived" and ministers representing local areas should be given leeway to vote against.

The government backs expansion, despite opposition from local residents and key political figures like Foreign Secretary Boris Johnson.

Mr Grayling is currently setting out the plans in the House of Commons - although its decisive vote is not expected until later in the month.

A decision - finally?

The debate on expanding Heathrow has been going on for nearly 20 years.

The last Labour government backed the idea, and won a vote on it in 2009, but that plan was scrapped - and the idea of expansion put on hold for five years - by the Conservative-Lib Dem coalition formed after the 2010 election.

But the idea of expansion was resurrected and has been subsequently backed by the Conservatives. Ministers approved a draft national airports policy statement in October setting out the conditions for a new runway, Parliament has yet to give its approval for detailed planning to begin.

Opponents have threatened a legal challenge while Mr Johnson, who is MP for Uxbridge and South Ruislip in west London, has vowed to "lie down in front of bulldozers" to prevent it.

If the plan is backed by the cabinet, Transport Secretary Chris Grayling could come forward with the statement later this week, possibly immediately, the BBC's Political Editor Laura Kuenssberg said.

With the Conservatives divided, she said Mrs May would be reliant on the support of Labour and the SNP to win the vote, which must take place within 21 sitting days of the statement's publication.

The BBC's assistant political editor Norman Smith said ministers whose constituencies would be directly affected might be given a "get out of a jail card" - by being allowed to miss the vote or even vote against.

• The chequered history of UK airport expansion
• In pictures: Heathrow airport
• Heathrow's death sentence for villages

'So expensive': Why are critics opposed?

Campaigners argue that a new runway will breach the UK's legal limits on air pollution and increase noise pollution with an extra 700 planes a day.

It will result in huge disruption to residents of nearby villages, such as Longford, Harmondsworth and Sipson, with hundreds of homes likely to be knocked down.

Robert Barnstone, from Stop Heathrow Expansion, told the BBC it was a "disappointing" day and the government was "failing people and failing the environment as well".

Ms Greening said the runway would cost £18bn to build and a further £15bn would have to be spent to upgrade local roads and other infrastructure, which passengers would end up footing the bill for.

The Putney MP, who backs expanding Gatwick instead, suggested the idea of Heathrow as a national hub airport was outdated and the focus should be on improving regional capacity and connectivity.

"We are now moving to point-to-point travel," she told BBC Radio 4's Today. "Why should people who are living in Newcastle spend hours travelling down to London, then fly out somewhere else.

"There is nothing national about this national policy statement. It is just a runway in Heathrow."

Ex-transport minister Theresa Villiers told BBC Breakfast it was going to be "another quite difficult day" for her colleague, Mr Grayling - who has faced criticism over the performance of the rail network since timetable changes came into force last month.

'Right for UK PLC'

Heathrow's owners say the airport is virtually full and a new runway, which is hoped would be operational between 2025 and 2030, would increase its capacity from 85.5 million to 130 million passengers.

The expansion is estimated to create about 60,000 new jobs and generate about £70bn in total economic benefits by the 2050s.

John Glen, Economic Secretary to the Treasury and City Minister, told BBC Radio 4's Today programme ministers had looked at "all the dimensions" of the project.

He said: "It is right that the government has looked at all the concerns around the environmental effect, but from the perspective of UK PLC we need to expand our capacity and this is the right thing to do."

Sir Howard Davies, whose 2015 review recommended a new runway as long as environmental and community impacts were addressed, said "significant" concessions had been made on reducing early morning flights and minimising the impact on residents on the proposed flight path.

Modern planes were less noisy and polluting, he told BBC Radio 4's Today programme, meaning airports were "gradually becoming friendlier neighbours".

The political battle - by Laura Kuenssberg, BBC political editor

Yes, the decades-long debate about airports in Britain is returning (it's never gone for long) just at a time when the government is embroiled in rows it will struggle to win. As one cabinet minister joked, "it's the gift that keeps on giving".

However, with only Boris Johnson having big doubts around the cabinet table, the real rumpus will be in the Parliamentary Tory Party.

Plenty of Tory MPs have long held objections to Heathrow and they will be made loudly on the backbenches in the weeks to come. The government doesn't have a majority and remember, it wants to get this plan through the Commons by the end of the month.

If they can, it will be a demonstration of "look, we are getting on with things, it's not just Brexit!"

There will be howls, and the process even after this likely vote is a very long one. But the government can expect to get the vote through. Even if Labour opposes it, which it may well do on environmental grounds, the party is also split on the merits of the project so might not all vote together.

Read the rest of the blog

Will Labour come to government's rescue?

Labour has said expanded capacity is vital to the UK economy but its support is conditional on tests being met on capacity, climate change, noise and air quality, as well as the wider economic benefits.

But there is also a split in opinion when it comes to individual MPs, with shadow chancellor John McDonnell - whose Hayes and Harlington constituency could see homes demolished - is opposed.

Mike Gapes, Labour MP for Ilford South, said the economic case for the runway is clear and consecutive governments had been "dithering and delaying for more than 20 years".

But his colleague Ruth Cadbury, Labour MP for Brentford and Isleworth - near to Heathrow - said it would result in fewer long-haul routes to other English airports and less transport investment outside the south-east.

Lib Dem leader Sir Vince Cable said the plans were an "expensive folly" and his party's 12 MPs would work with others to "put an end to this project once and for all".

The carbon question

As one would expect, there have been contrasting reactions from business and environmental groups.

London First, which speaks on behalf of firms in the capital, said the investment and employment case for a new runway was "proven".

It urged MPs to back the government and support the "thousands of businesses who need these new connections".

But Greenpeace said a new runway was not compatible with building a low-carbon economy.

"This airstrip alone will load the atmosphere with as much extra carbon as some entire countries pump out," said the campaign group's executive director John Sauven.

Source: BBC News