Extinction Rebellion activists are threatening to shut down Heathrow Airport with drones.
The climate change protest group vowed to stage a one-day demonstration in June and then 10 further days in July – unless the government cancels plans for expanding the airport.
Ten days of protests across central London in April saw 1,130 people arrested for various offences.
Heathrow Airport said the plan was “reckless” and could “endanger lives”.
Extinction Rebellion said it was in talks with its members about carrying out “nonviolent direct action to ensure Heathrow authorities close the airport” on 18 June.
It said it would “act to shut the airport down for up to 10 days from 1 July” if the government does not cancel all Heathrow expansion.
The plan to use drones was revealed in a leaked consultation document shared between group members.
A Heathrow spokesman said: “This is reckless action that if carried out could endanger the lives of the travelling public and our colleagues.
“We agree with the need to act on climate change, but that requires us to work together constructively – not commit serious criminal offences just as hard-working people prepare to spend a well-earned holiday with their family and friends.”
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Aviation Minister Baroness Vere warned that any illegal activity “must be met with the full force of the law”.
She added: “Flying drones near an airport is a serious criminal offence and using drones to deliberately put people’s safety at risk carries a maximum life sentence.
“No government has done more to reduce carbon emissions and Britain is at the forefront of global efforts to tackle climate change.”