By Mike Pearse, Transport Correspondent
The Government will tomorrow make a decision on where a new runway for the south should be built and Heathrow is expected to be the winner.
But it is expected that Gatwick could also be allowed to expand at a later date. The decision will then be subject to consultation ahead of a vote by MP's in early 2018.
The decision will bring to an end a debate going back fifty years and with it new rows. Whichever airport is selected is likely to lead to campaigners going to court to try to stop the plan.
At both airports views are divided.
Those who support the plans say they will create tens of thousands of jobs and boost the economy, particularly post-Brexit, when we need to be connected to all parts of the world.
Campaigners against say there will be hundreds of thousands more flights with extra noise and emissions.
Airlines will welcome the news but say it should not be at the cost of increased airport fees to pay for it. IAG, the owner of British Airways, say an extra £40 could be added to a return fare by the expansion at Heathrow, which will cost £17.6 billion.
The decision is the start of the planning process and not the beginning of the diggers.
Consultation, planning inquiries and court reviews mean the earliest the new runway could open is 2025. And the plan at Heathrow means putting the M25 in a tunnel so the new runway can run over it. That will be a challenge.
At Gatwick 200 properties will need to be demolished. At Heathrow it is nearer 800. A property compensation scheme will give those affected the opportunity to sell at above the market rate.
One key issue will be the ability for hundreds of thousands more flights but keeping emissions in line with tough new targets.
Both airports plan major new transport hubs for rail to get passengers onto public transport. Reading could see a new rail link to Heathrow taking just 26 minutes. Heathrow could introduce congestion charging to persuade more use of public transport.
There will be plenty of political rows. Richmond MP Zac Goldsmith says he will resign if Heathrow goes ahead. Some members of the Cabinet are also against the plans including Justine Greening, Boris Johnson and Philip Hammond. Prime Minister Theresa May, Maidenhead MP, was herself once against the expansion of Heathrow, which her opponents are likely to remind her of in a bid to try and embarrass her.
With airport capacity fast running out a decision is at last being made. But history has shown it has been difficult. In 2009 a third Heathrow runway was approved by the Labour Government. The Conservatives who won the next election set up the Airports Commision to review it.
They came up with two options at Heathrow - a new runway and extending an existing one - or a new runway at Gatwick.
Tomorrow will see the latest twist in the debate and the start of a major new battle.
The main Heathrow plan is for new runway north of the existing airport near the M4.
The new runway will cost £17.6 billion pounds.
The number of flights will rise from 480,000 a year - to 740,000.
It'll be open in 2024 or 2025. But to build it means demolishing 783 homes in nearby villages.
Campaigners say an extra 300,000 people a year will end up living under new flight paths.
The runway will create 72,000 local jobs - and that means 40,000 new homes will be needed, many in Berkshire, Buckinghamshire, Oxfordshire and north Hampshire.
There will be extra pressure on roads and rail - as passenger numbers rise from 75 million today - to 150 million, each year, by 2050.
There is currently only one runway at Gatwick, the busiest single runway airport in the world. Under the plan the second runway and a new terminal will to the south of the existing one.
Gatwick say it will cost £7.8 billion pounds and will be around 3,000 metres long.
But it will mean the demolition of 202 properties to make way for it. The plan is for it to open in 2025.
Gatwick say nationally it will create 120,00 new jobs and boost the economy by £40 billion.
Flight numbers will rise from 271,000 a year up to 560,000 by 2040.
Its claimed an extra 37,000 people would be affected by noise.
Locally Gatwick say the plan will create 22,000 jobs.But it will put pressure on local infrastructure. Its estimated up to 45,000 new homes will be needed - many in Sussex, Surrey and Kent.
Gatwick say there will be a boost to the local economy across the south east of £1.7 billion.
There will also be pressure on the roads and rail network with passenger numbers of 42 million today rising to around 95 million by 2050.