Unions have joined forces with company directors to warn that 140,000 jobs are at risk without urgent action to increase the UK's aviation capacity.
Tourism, exports and foreign investment will also be hit over the next decade unless the Government supports the expansion of Heathrow, according to new research.
The GMB and Unite unions, supported by the Institute of Directors, said they were joining a growing coalition of groups to highlight the economic dangers of failing to tackle the UK's "connectivity crunch".
The new study, by Oxford Economics, said the UK economy could be losing £8.5 billion a year by 2021 unless something is done to help businesses access world markets via a hub airport.
The research said that constraints on capacity at Heathrow will result in up to 5.8 million fewer international visitors to the UK from long-haul destinations each year by 2021.
Developing a new hub in the Thames Estuary would take 25 years, during which time even more jobs will have been lost, the Government was warned.
Mick Rix, national officer of the GMB, said: "It is plain daft to exclude the option of expanding Heathrow. Last autumn the Government said it was looking at another airport hub in the South of England, but not at Heathrow. GMB consider that this is profoundly wrong and call on all political parties to keep every option on the table, including the issue of the third runway at Heathrow."
Len McCluskey, Unite's general secretary, said: "It is madness to think that the UK can muddle on without a top-quality international hub airport."
A Department for Transport spokesman said: "These assertions are based on a draft report which is yet to be published, so it is difficult to agree or disagree with its supposed findings.
"The Government will consult on an overarching sustainable framework for UK aviation this spring and alongside this we will publish a call for evidence on maintaining the UK's international aviation connectivity."