A Gatwick spokesman has said the West Sussex airport will continue to prepare for expansion, even if it is not chosen by the UK government for a third runway over Heathrow.
The rationale behind this, the spokesman told the Press Association, was the improbability of the Heathrow project overcoming the many challenges against it, even if government gave it the all-clear.
Though the Airport Commission has recommended Heathrow as the best site for a new runway, it will be for government to ultimately vote on the decision.
The controversial decision also has implications for the Prime Minister Theresa May's constituency Maidenhead in Berkshire, which is close to the Heathrow site.
The spokesperson, who has not been named, apparently told the Press Association: "Gatwick would be standing ready to deliver the new [second] runway as, should Heathrow get the green light, it is likely to fail as it has several times before.
"A decision on next steps will be taken after the government announcement on new runway capacity. While Gatwick does not rule out launching legal action, other groups have already said they would if Heathrow expansion is green-lighted."
Earlier in the year, Gatwick Airport chief executive Stewart Wingate promised the government that if Gatwick were chosen, he promised "spades in the ground before 2020", with the terminal operational by 2025. He also questioned some of the assumptions made by Sir Howard Davies' Airports Commission report.
Heathrow Airport published a poll earlier this year, revealing that more than two-thirds of MPs would support the third runway. However, many environmental groups as well as MPs such as Zac Goldsmith and Foreign Secretary Boris Johnson, as well as the Mayor of London Sadiq Khan, object citing concerns such as poor air quality in the London area.
Meanwhile, Chancellor of the Exchequer Philip Hammond, who is also a former transport secretary, declared support for Gatwick several years ago.