Two people have been arrested in connection with the “criminal use of drones” that caused chaos at Gatwick Airport, with reports out of Britain saying a keen-eyed passerby may have played a key role in the investigation.

The drones have caused massive disruption to Christmas traffic at Britain’s second-busiest airport since Wednesday, affecting tens of thousands of passengers and plunging Europe’s air routes into chaos as planes were diverted and flights cancelled.

“As part of our ongoing investigations into the criminal use of drones which has severely disrupted flights in and out of Gatwick Airport, Sussex Police made two arrests just after 10pm on 21 December,” Superintendent James Collis said in a statement.

The arrest of the couple, identified as glazier Paul Gait, 47, and his wife Elaine Kirk, 54, stunned Mr Gait’s employer, John Allard, who told the Telegraph he is convinced police have arrested the wrong man.

He was “part of a three-man team fitting glass doors and windows in the Crowborough area”, at the times drones were buzzing the airport, Mr Allard said.

The Sun newspaper reports motorist Paul Motts was delivering a package on an isolated country lane about four miles from Gatwick when he spotted a man and woman disassembling two drones.

“It was a big thing with lights on its arms and roughly 4ft across,” Mr Motts said.

“He had a smaller drone, about 2ft across, next to him.

“He was leaning over and doing something to it. He was totally focused and did not look up when I drove past.

“It looked like he was packing the drones away. Two minutes later we turned around and came across him cycling away.”

Superintendent Collis said the arrests, reported to be a man and a woman, came after a late-night raid on a home “in the Gatwick area” as part of what Scotland Yard has dubbed Operation Trebor,

Armed troops and police threw a cordon around Gatwick, one of Europe’s busiest airports, after the “commercial size” drones continued to reappear above the runway, stranding thousands of Christmas travellers.

As distressed and angry passengers waited at Gatwick, 50 kilometres south of London, Prime Minister Theresa May threatened jail time for anyone caught “endangering aircraft”.

“The activity we have seen is illegal and those who are caught endangering aircraft can face up to five years in prison,” she said.

While police said there was no indication of a terrorism motive behind the disruption, which began on Wednesday night, British media have reported speculation by unnamed investigators that the drones were operated by environmental activists who have disrupted airports in the past.

“The very fact that environmentalist activists are under suspicion is interesting in itself, for it is true that the shutdown would have meant that thousands of tonnes of CO2 emissions were prevented, albeit for only a day, before normal business resumed,” writes The Independent‘s Roger Tyers.

“If yesterday’s events at Gatwick make at least some of us stop and think about the pollution from air travel, that is no bad thing.”

Frustrated, angry and inconvenienced travellers would disgree. Gatwick had to cancel all the staggering total of 760 departures and landings since Thursday.

The departures board at Gatwick paints a sad picture as passengers wait out the drone crisis. Photo: AAP

A total of about 110,000 passengers were affected, said Gatwick’s chief operating officer Chris Woodroofe, who added that authorities rejected shooting the drones out of the air for fear of casualties caused by stray bullets.

“The police advice is that it would be dangerous to seek to shoot the drone down because of what may happen to the stray bullets,” he told BBC radio.

Transport minister Chris Grayling said it was clearly a deliberate act.

“This is a commercial-sized drone,” he said.

“Every time Gatwick tries to reopen the runway, the drones reappear.”

Passengers stranded at Gatwick waiting for updates on their travel options. Photo: Getty

Georgia-bound passenger Ani Kochiashvili spent six hours overnight sitting on a plane with her children.

“I’m very annoyed because I’m with two kids, a three-month-old and three-year-old,” she told Reuters by phone.

“They require a lot of space and food and changing and all that, and the airport is crazy busy so it’s challenging.”

Prime Minister Theresa May condemned the drone flights as “irresponsible and completely unacceptable”, adding that police may be given greater powers against drones in the future.

“I feel for all those passengers whose travel plans have been disrupted by this drone activity and the action that has had to be taken in response to it. At this particular time of year this is particularly difficult for people.

“We have already passed legislation in relation to the use of drones. As it has been made clear, the activity we have seen is illegal and those who are caught endangering aircraft can face up to five years in prison. And we’re consulting on further aspects of this including further police powers.

“We will continue to work with the Gatwick authorities in order to bring this to a close such that people will be able to get on to the travel that they were expecting over the Christmas,” Ms May said.

The airport and its biggest airline, easyJet told, passengers to check before heading to the terminal, where people sat waiting on stairs and floors.

A Police helicopter flies over Gatwick Airport as they search for the Drone operator. Photo: Getty

Drone expert Peter Lee, of Portsmouth University, said he and others had been anticipating disruption.

“An airport would be a preferred or obvious target for somebody who wants to either just create mischief or criminal damage,” he said.

“One of my concerns about today is that it may well encourage copy-cat incidents because you can achieve a high amount of disruption for a very, very low cost.”

Even after Gatwick re-opens, the backlog and disruption are expected to last for days.

Gatwick said that it was working with its airlines, the biggest of which also include British Airways and Norwegian, on recovery plans once the runway re-opens.

It apologised on Twitter to passengers, adding that safety was its “foremost priority”.

Gatwick, which competes with Europe’s busiest airport Heathrow, west of London, had previously said that Sunday would be its busiest day of the festive period.

-with AAP