“The British government’s approach is that we want to be sympathetic to, hospitable to, the drone industry,” said David Dunn, an expert in international security at the University of Birmingham. “Part of the nervousness, the reluctance in bringing in new regulation is not to kill what they see as a potential golden goose.”

Government ministers said they would hold talks with airports about how to deal with future incidents. But Professor Dunn said he had met with cabinet ministers, spoken to transportation officials and given testimony to parliamentary committees about measures the government should consider — all with little to show for it.

“You try, and it feels like you’re hitting your head against the brick wall,” he said.

On Friday, the police said they had identified “persons of interest” in the drone flights but offered few clues about the motive beyond saying that the incursions were deliberate. Assistant Chief Constable Steve Barry of the Sussex Police said there was “no evidence” that the drone incursions were state-sponsored, adding that they could be the result of “high-end criminal behavior” or “individuals trying to be malicious.”

At least 150 flights were canceled on Friday, causing a ripple effect elsewhere in Europe, after 800 flights had been halted earlier in the week. In all, upward of 100,000 passengers were affected.

The discount airline easyJet said that runway movements had been “restricted to a limited number per hour” and, like other airlines, warned passengers on Friday night to confirm the status of their flight before leaving for the airport. Still, the scene at Gatwick on Friday was much calmer than in previous days, when frustrated and frantic passengers packed its two terminals.

Drone industry executives and aviation experts said the systems at Gatwick, as at many airports, were overmatched for monitoring and warding off drones. The military was likely to have used more sophisticated surveillance equipment, like air defense radars or thermal-imaging devices, said Philip Ingram, a former colonel in British military intelligence.