The runway would cost pound21 billion, with flights expected to take off within a decade, while the rest of the privately-funded investment will go toward expanding and modernising the airport.

Heathrow, Europe's busiest airport by passenger numbers, said the expansion would provide at least 30 new daily routes, more domestic connections and improved flight times.

The increased capacity would almost double the number of annual passengers from 84 million currently to up to 150 million passengers annually.

"It has never been more important or urgent to expand Heathrow," said chief executive Thomas Woldbye.

"We are effectively operating at capacity to the detriment of trade and connectivity," he added.

Despite fierce opposition from environmentalists and local residents, London mayor Sadiq Khan and some Labour MPs, the Labour government backed the new runway in January in a bid to boost UK economic growth.

It would be a rare expansion in Europe, where countries are split between efforts to reduce greenhouse gas emissions and the needs of a strategic sector that has seen demand grow.

Heathrow has submitted its proposal for the 3,500 metre runway to the UK government, which has also invited a rival proposal.

- Green trade-offs -

Heathrow's proposal includes pound12 billion to fund a new terminal and pound15 billion for modernisation.

"A third runway and supporting infrastructure can be ready within a decade, and the full investment across all terminals would take place over the coming decades," Heathrow said in a statement.

UK Prime Minister Keir Starmer is determined to deliver major infrastructure projects to revive the UK economy that has struggled to take off since the party came to power a year ago.

The government is expected to also back expansion at Gatwick airport, south of the capital, in October -- having recently approved upgrades to London's Stansted, Luton and City airports.

Britain's Supreme Court ruled at the end of 2020 that Heathrow could build the third runway, overturning a legal decision to block construction on environmental grounds.

Local residents "will see their lives put on hold for a few more years while more money and time is wasted on a doomed scheme," said Douglas Parr, policy director for Greenpeace UK.

He added the plans "export more tourism wealth out of the UK in the most polluting way possible."

Arora Group, one of Heathrow's largest landowners, on Thursday said it will submit a rival bid to build a shorter third runway, promising lower costs and less disruption to local residents and the environment.

"This is the ?rst time the government has invited a competing proposal for Heathrow expansion," the UK-based property and hotel firm said in a statement.

British Airways owner IAG's chief executive Luis Gallego said the rival bid was "credible" as the group announced its net profit jumped 44 percent to 1.3 billion euros ($1.5 billion) in the first six months of the year on "strong demand".

"We always think that competition is good to improve things, and we have seen that in commercial aviation in the past," he added.

Airport-owner Heathrow's latest investment proposal comes in addition to plans to invest pound10 billion over the next five years in upgrades to boost passenger numbers, which would be largely funded by higher charges on airlines.