Theresa May has been urged to give the green light to a new runway at Heathrow by 50 home nations' politicians who describe the airport as "our gateway to the world".
The Prime Minister is due to make a decision imminently and is very unlikely to back a compromise option of new runways at both Heathrow and Gatwick, it is understood.
The decision is highly politically sensitive given the opposition to Heathrow expansion within her own Cabinet and party, and it was repeatedly delayed by her predecessor David Cameron.
Now MPs and representatives from the devolved assemblies in Scotland, Wales and Northern Ireland have called on the PM to back expansion of the west London hub.
The group, which includes MPs such as Welsh former Cabinet minister Stephen Crabb, Northern Irish DUP deputy leader Nigel Dodds and Welsh Labour's Stephen Kinnock, wrote in a letter to Mrs May: "Although Heathrow is in London, it is the UK's hub airport.
"Other countries are investing in and supporting their hub, or looking on enviously as they hub through other countries.
"Northern Ireland, Scotland and Wales all have our own successful and growing airports.
"But Heathrow is our gateway to the world, bringing tourists to our attractions and helping our exporters reach new markets.
"Whether we are connected by road, rail or air, we know that connections to Heathrow are a key driver of investment decisions.
"Expanding Heathrow will create nearly four times more jobs in our three nations than other options being considered.
"Heathrow expansion is important for each of our nations remaining open, outward-looking, and trading globally.
"We urge you to act in the interests of all the nations of the UK and urgently approve the expansion of Heathrow."
Mrs May's Cabinet sub-committee on airports is due to meet very shortly, possibly as early as this week, to examine the arguments for the three options set out in last year's Airports Commission report.
The Commission recommended in July 2015 that a third runway should be built at Heathrow.
Other shortlisted options are extending the airport's existing northern runway or building a second runway at Gatwick.
Tory MP Zac Goldsmith has warned Mrs May she faces losing Conservative MPs and councils if she goes for Heathrow.
The unsuccessful London mayoral candidate, who has promised to quit the Commons if Mrs May goes for Heathrow, said expanding the west-London hub would prove to be a "political millstone" for the Prime Minister.
Writing in The Sunday Telegraph, he said: "There is no doubt that despite huge gains against the Liberal Democrats in west London in recent years, the Conservative Party would be badly damaged in the event that Heathrow gets a green light.
"I promised voters I would step down and hold a by-election if Heathrow gets the go-ahead and I will stand by that pledge, but the fallout will be much wider, and it will be hard for our brilliant local councils to weather the storm.
"That's not just a party issue. If I were investing in Heathrow, it would worry me greatly because there is a very real risk that as soon as the polls tighten, the party will feel the need to reverse its policy, yet again."