A man and woman were being questioned by police over the “criminal use of drones” as Gatwick airport slowly returned to normal after days of Christmas travel chaos.

Following the most disruptive incident ever caused by a drone at a major international airport, detectives continued to interview a 47-year-old man and a 54-year-old woman from Crawley as forensic officers searched a house in the West Sussex town, three miles south of Gatwick.

A series of drone sightings above its runway had forced Britain’s second-largest airport to shut three times in three days, leaving around 140,000 passengers stranded. It was the airport’s biggest disruption since the Icelandic volcanic ash cloud of 2010.

Terminals at Gatwick were broadly back to normal last night with the airport on course to run “a full schedule” of 757 flights, carrying 124,484 passengers. “Safety is Gatwick’s top priority and we are grateful for passengers’ continued patience as we work to get them to their destination in time for Christmas,” said a spokesman.

Those arriving at the airport told a different story, however, describing delays of many hours involving road and ferry diversions. This was the knock-on effect of more than 1,000 flights being cancelled or diverted during the 36 hours of disruption at what is the world’s second-busiest single-runway airport.

The man and woman are being questioned “on suspicion of disrupting services of civil aviation in a way likely to endanger the safety of operations or persons” – offences that carry a maximum sentence of life imprisonment on conviction.

Although police released no further details, officers urged the public to be vigilant amid efforts to “build resilience to detect and mitigate further incursions from drones”.

Elsewhere, the debate continues on why the airspace was not secured until Thursday night, when the army deployed unidentified military technology – and how a drone seemingly managed to breach the airport defences briefly on Friday evening, prompting further delays.

Among military equipment said to have been deployed is the Israeli-developed Drone Dome system, which can pinpoint drones by radar.

The scale of the disruption has focused attention on current legislation, amid claims that transport secretary Chris Grayling sidelined plans to introduce laws regulating drone use, despite being repeatedly warned of the risk they posed.

Yet the Observer has learnt that six UK airports will begin trialling new counter-drone technology early next year as authorities and airports scramble to deflect blame for the Gatwick chaos. The trials, run in conjunction with the National Air Traffic Services, will see the six airports, which do not include Gatwick, provided with technology allowing them to spot drones, including rogue ones, and alert the police.

“We will be testing it in six airports and hopefully it will last a few months and then go out to all Nats airports,” said Richard Parker founder and CEO of Altitude Angel, a technology company involved in the pilot project. But the length of time it has taken airports to wake up to the threat is likely to raise questions.

Last week’s disruption has also highlighted Britain’s sluggishness about a drone registry, say analysts. Since 2015, the US Federal Aviation Administration has required drone operators to be registered, allowing the devices to be identified.

Of more immediate concern to thousands of passengers is the question of compensation. Airlines said they were not obliged to pay out as the situation was outside their control. They are advising passengers to contact their travel insurer, but insurance companies are telling people to speak first to their airline.

Travel insurance policies differ, and many passengers will not be covered. Which? said passengers should be able to claim “for losses they incur” on their travel insurance.

However, the Association of British Insurers said people affected by disruption at Gatwick should approach the airlines for refunds, but that it depends whether travellers also purchased travel insurance which includes cover for disruption.

AXA, which provides insurance plans for passengers on various airlines, also urged people to approach airlines “in the first instance”. On its website, it reiterates that flight delays and cancellations are covered only if you have travel disruption cover, which many AXA policies include.

The Civil Aviation Authority has said airlines are not obliged to pay compensation for delays since events were outside their control. However, an industry source said they still have a duty of care to customers, meaning they should either provide refunds or put people on alternative flights.

Grayling has said the government will be speaking with the insurance industry to make sure it takes an “enlightened view”.

At the height of the disruption, thousands were forced to spend the night at the airport, where staff provided free water, blankets and food.

The financial impact to the airlines is not yet clear with Gatwick’s biggest operators – including easyJet, British Airways and Norwegian – saying it is too early to ascertain its damage.