Gatwick is poised to reveal a new plan to create a second runway enabling it to handle up to 84,000 extra flights a year.
The airport previously submitted a proposal to build an entirely new runway two years ago, which was rejected by the government.
Approval was then given for a third runway at Heathrow.
Gatwick’s plan is due to be showcased in a draft masterplan, which will be published on Thursday.
It involves using the airport’s existing emergency runway so a costly building project would not be required, the Sunday Times reported.
After the previous plans were rejected, Gatwick, which handles around 282,000 flights a year, said it would put together new growth plans using “existing infrastructure”.
The masterplan will include the proposed ‘routine’ use of its 8,400ft emergency runway.
Gatwick would require planning permission from the Civil Aviation Authority to use its standby runway.
The runway, which is normally used as a taxiway or an alternative when the main runway requires maintenance, runs parallel to the 10,800ft main runway.
A legal agreement from 1979 that prevents the runways being used concurrently expires next August.
The emergency runway, which is normally used as a taxiway or an alternative when the main runway requires maintenance, is understood to be primed for use by smaller, short-haul aircraft.
This could boost the airport’s capacity by between 20% and 30%, adding up to 231 extra flights a day.
The runway could potentially be used after 2023, before Heathrow completes its third runway in 2026.
It is believed that Gatwick will be seek to use the emergency runway as an interim plan for growth.
But campaign group Communities Against Gatwick Noise and Emissions (GAGNE) said: “This is simply betrayal of communities of Sussex, Surrey and Kent who have already endured the increases in long-haul movements this year by 24.1% – this is a second runway by the backdoor, how can communities ever trust Gatwick management again?“
Gatwick said any new development “would be fully compliant with all international safety requirements”.
A Gatwick spokesman said: “Airports are required to publish new master plans every five years, setting out their future growth plans and Gatwick has consistently confirmed it will do so before the end of this year. The draft plan will set out for our local communities, partners, airlines and stakeholders three possible growth scenarios, which we will then open up for views and feedback.
“In line with recent government policy, Gatwick has previously set out it is exploring how to make best use of its existing runways, including the possibility of bringing its existing standby runway into routine use. This would deliver an incremental increase in capacity that complements the expansion schemes of other airports across the south-east.
“Safety and security are always our key priorities and any new development would be fully compliant with all international safety requirements.”
Brian Strutton, general secretary of the British Airline Pilots Association, said: “Balpa has always been in favour of extra capacity across the UK, and with Heathrow and Gatwick already running pretty much at full capacity, something needs to be done soon.
“If it is approved by the regulators and complies with safety rules, then by using its emergency runway Gatwick can provide much-needed capacity in the south east, which we would welcome.
“We also urge the government to hurry up with a final decision on Heathrow expansion, which we believe will be even more vital in a post-Brexit UK to support our thriving aviation industry.”
Holiday Extras Group CEO Matthew Pack said: “Figures from 2017 show that, despite the government rejected Gatwick airport’s plans to build a second runway in 2016, Gatwick’s long-haul operations have increased to facilitate hundreds of thousands more passengers that are taking these routes.
“If, as the Sunday Times reports, a ‘second’ emergency runway could be used for short-haul flights, this could help free up space to facilitate the increased demand for long haul flights from passengers around West Sussex and beyond.
“Not only would this allow the airport to offer more services to these kinds of destinations, but it is also likely that more jobs will be created in the local area. As a country, we’d also benefit from all the additional visitors from long-haul destinations too.”
Meanwhile, Gatwick’s major shareholder Global Infrastructure Partners is reported to be considering selling some or all of its 42% stake in the airport which could raise up to £10 billion.
Gatwick handles 45 million passengers a year