Failure to keep a major hub airport could cost the UK up to one million front-of-the-aircraft passengers a year, Heathrow bosses are expected to say tomorrow.
The claim will be made by Heathrow chief executive Colin Matthews as he presents a report entitled One Hub or None.
The possible one million lost passengers are those that fly in the first-class and business-class seats on flights through Heathrow.
At present, Heathrow is the UK's major hub airport and the need for a major hub forms part of the Whitehall-appointed Aviation Commission which is being headed by former Financial Services Authority chief Sir Howard Davies.
Heathrow's hub report is being sent to Sir Howard, whose team will present an interim report on aviation policy to the Government by the end of next year and a final report in summer 2015.
Mr Matthews is expected to argue that splitting a hub between Heathrow and Gatwick - the so-called Heathwick option - is not practical and that building up other airports as major hubs would not work either.
The aviation policy debate is set to be a fierce one, and likely to run and run. London Mayor Boris Johnson, who is dead against an extra, third, runway at Heathrow, favours a new Thames Estuary airport or possible expansion at Stansted.
The estuary so-called "Boris Island" scheme gained little support from MPs in a poll earlier this week.
Of the 93 MPs surveyed, 46% supported expansion at Heathrow, with only 16% backing the estuary plan.
Mr Johnson has also been highly critical of the Government's timescale for the Davies Commission, arguing that firm policy decisions should have been asked for far earlier than at a point beyond the next general election.
Sir Howard's team's initial report will focus on just what can be done to cope with aviation demand in the immediate future.
The all-party 2M Group, which represents more than 20 local councils close to Heathrow, has said that it will be telling the Davies Commission that loosening restrictions on Heathrow's existing runways would destroy the quality of life for flightpath communities on all sides of the west London airport.
The group wants a guarantee that "runway alternation" and night-flight restrictions will not be sacrificed so the airport can handle more planes.
The campaign group says that allowing both runways to be used in tandem for arrivals and departures - a system called "mixed mode" - would be just as damaging as creating a third and fourth landing strip.