George Osborne has urged the Government to back the expansion of Heathrow Airport.
The former chancellor said the west London hub needs increased capacity so that Britain can be "outward-looking, free-trading and global".
Reports emerged on Thursday that ministers could back expansion at both Heathrow and Gatwick.
Mr Osborne claimed that although building a second runway at the latter could be considered, it should not happen at the same time as Heathrow expansion.
In a series of Twitter messages, the Tory MP for Tatton wrote: "Time for a decision on airports and go for Heathrow.
"Economic case overwhelming. Connects Northern Powerhouse. Ensures Britain is open to world.
"If we want Britain to be outward-looking, free-trading and global, we must expand the great airport that connects us to that world and that trade.
"We can consider Gatwick expansion. But not at the expense of Heathrow - and not in parallel or else, in practice, nothing will get built."
Prime Minister Theresa May confirmed last week that the Government would "shortly announce" a decision on which expansion project will get the go-ahead.
The Davies Commission recommended in July last year 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."
Greenpeace UK executive director John Sauven described expansion of both Heathrow and Gatwick as "the worst of both worlds".
He said: "We can only hope these rumours are not true.
"An increase in air traffic on this scale will make climate change and air pollution targets virtually impossible to meet."
Sarah Clayton, co-ordinator at AirportWatch, an umbrella group of environmental organisations and community groups, said: "It's the most crazy time for the Government to be building a runway, they've got Brexit, no idea what's happening with the pound, with the economy.
"The whole thing is a madness."
She suggested that if both airports got the go-ahead for a new runway, then it would mean Gatwick would not be able to expand as it would lose out in competition with Heathrow for airlines.
And if the runways were built, it would entail billions of pounds of spending on infrastructure which would have to be paid for by the taxpayer, she said.
Of communities near Gatwick and Heathrow, and under their flight paths, Ms Clayton said: "People are really scared, they're genuinely distraught."
Aviation minister Lord Ahmad, asked in the House of Lords earlier this week whether the Government will consider supporting one of the two Heathrow options as well as Gatwick, replied: "As far as expansion is concerned, the Commission reported back on the need to increase capacity by 2030 with the addition of one runway in the South East, and that is where the Government's decision is focused."