London Heathrow Airport remained fully operational Sept. 13 despite attempts by climate change activists to disrupt flights by flying small unmanned aerial vehicles (UAVs) within the airport’s exclusion zone.

Twelve people have been arrested “on suspicion of conspiracy to commit a public nuisance,” London police said in a statement. There has been no breach of airport security and all 12 were being held in custody, the police said.

The protest group, Heathrow Pause, threatened to shut down the airport for days by flying small drones at no higher than head height within the 5 km (3.1 mi.) exclusion zone, where UAV flights are illegal, then turn themselves in to the police. The group said the drones would not pose a threat to aircraft, but Heathrow’s policies would require it to halt flights if UAVs were known to be active in the area.

The group opposes construction of a third runway at Heathrow and said it is attempting to raise awareness of aviation’s impact on the environment.

In a statement, Heathrow said runways and taxiways “remain open and fully operational despite attempts to disrupt the airport through the illegal use of drones in protest nearby. We will continue to work with the authorities to carry out dynamic risk assessment programs and keep our passengers flying safely on their journeys today.

“We agree with the need for climate change action, but illegal protest activity designed with the intention of disrupting thousands of people, is not the answer. The answer to climate change is in constructive engagement and working together to address the issue, something that Heathrow remains strongly committed to do.” 

UK media reported that jamming equipment is being used to prevent drone flights near the airport. A Heathrow spokeswoman said the airport does not comment on security processes.

Police made seven arrests Sept. 12 “in relation to protest activity taking place in the vicinity of Heathrow Airport” and arrested more five people Sept. 13—four on public land outside the airport perimeter and one within the airport.

Metropolitan Police told ATW around 6 p.m. local time that none of those arrested had been formally charged with an offense and that under the Police and Criminal Evidence Act, those arrested could be held for a maximum of 24 hours.

On Heathrow Pause’s Twitter feed Sept. 13, the group said four of its members who had been “arrested preemptively”—three drone pilots and the group’s press officer—had been released around 5 p.m. local time and more were expected to be released within hours.

Alan Dron,