Gatwick has been given a qualified green light to operate a second runway after the government “set out a path to expansion” for London’s second biggest airport.

The deadline for the government to make a final decision has been extended to late October, but the transport secretary, Heidi Alexander, has issued a “minded to approve” letter to Gatwick for the £2.2bn expansion scheme. The project could allow more than 100,000 extra flights a year at the West Sussex airport.

Planning inspectors had recommended rejecting Gatwick’s project, which will modify an emergency runway and taxiway to be used alongside its existing main runway, but suggested it could be approved if conditions on noise and public transport access to the airport were met.

In a report submitted to the transport secretary in November, inspectors found the proposals “would undoubtedly result in both local and national economic growth” but “the scale of greenhouse gas emissions arising would … have a material effect on achieving carbon targets”.

The airport will have until a new deadline of 24 April to accept further conditions for the scheme to go ahead, and the government has until 27 October to make a decision.

In a written statement to parliament, Alexander said the planning inspectors had recommended an alternative option “which includes a range of controls on the operation of the scheme”.

She said that as “not all the provisions have been considered during the examination, I am issuing a minded to approve decision that provides some additional time to seek views from all parties on the provisions, prior to a final decision”.

A government source said: “The transport secretary has set out a path to approving the expansion of Gatwick today following the planning inspectorate’s recommendation to refuse the original application.

“Expansion will bring huge benefits for business and represents a victory for holidaymakers. We want to deliver this opportunity in line with our legal, environmental and climate obligations.

“We look forward to Gatwick’s response as they have indicated planes could take off from a new runway before the end of this parliament.”

Gatwick’s chief executive, Stewart Wingate, said he welcomed Alexander’s announcement, which “outlined a clear pathway to full approval later in the year”.

“It is vital that any planning conditions attached to the final approval enable us to make a decision to invest £2.2bn in this project and realise the full benefits of bringing the northern runway into routine use,” he said. “We will of course engage fully in the extended process for a final decision.”

The Conservatives accused the government of “kicking the can down the road”. The shadow transport secretary, Gareth Bacon, said: “Labour promised to go ‘further and faster’ on growth, but once again they are failing to deliver.”

According to Gatwick, the project will create 14,000 jobs and generate £1bn a year in economic benefits.

Wingate said the airport had “outlined to government how we plan to grow responsibly to meet increasing passenger demand, while minimising noise and environmental impacts”.

Local campaigners, however, have voiced a number of concerns. Beyond carbon emissions and noise, they include the impact on housing provision, wastewater treatment and potential congestion on local roads and rail.

The second runway, which will be long enough for typical short-haul passenger jets, will increase the airport’s annual number of flights to 380,000, with passenger numbers going up from 45 million to 75 million a year.

Gatwick first launched the scheme – described as a second runway by the backdoor by opponents – in 2018, soon after it lost out to Heathrow in seeking approval for expansion from the Airports Commission.

Rapid growth in air travel since the Covid pandemic has led a number of airports to seek expansion, and the Labour government, particularly the chancellor, Rachel Reeves, has signalled its backing for the industry to grow, in the face of environmental concerns. Alexander told an industry dinner earlier this week that she loved flying and was “ambitious for the sector”.

Heathrow will submit plans and policy demands for a third runway this summer, while Luton airport’s development plans are awaiting ministerial signoff by early April.

Local campaigners had signalled they would seek to overturn an approval by Alexander in the courts. Peter Barclay, the chair of the Gatwick Area Conservation Campaign, said: “We are calling out the government’s failure to recognise Gatwick’s false economic claims and its plans to fly in the face of climate breakdown.”

Environmental groups criticised the government’s support for Gatwick’s expansion.

Rosie Downes, the head of campaigns at Friends of the Earth, said: “At a time when we should be doubling down on climate action, given the weather extremes we’re seeing globally and near daily warnings that our planet’s health systems are at breaking point, signalling support for Gatwick’s expansion is totally bewildering.”

Alethea Warrington, the head of aviation at the climate charity Possible, said: “Giving the green light to yet another airport expansion is as economically clueless as it is environmentally destructive.”

After the government’s support for Heathrow’s third runway, the airport’s major shareholder Ardian, a French private equity group, has increased its shareholding to almost a third.

It finalised a deal to buy a further 10% stake, including the final holdings of Ferrovial, the Spanish infrastructure group that for many years was the dominant partner on the board.