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Blocking the M25 motorway is a "legitimate" and "reasonable" means of demonstrating about climate issues, the Green Party's MP has told Sky News.
Government ministers have urged police to take "swift" action to clear roads of protesters, after the London orbital motorway was blocked repeatedly in a week.
Numerous arrests were made on Friday as demonstrators from the Insulate Britain group targeted M25 junctions in Kent, Surrey and Essex.
Home Secretary Priti Patel this week condemned the "guerrilla tactics" of the protestors as "selfish" and said they "detract" from their calls for greater UK action on home insulation.
And Transport Secretary Grant Shapps has branded the group's actions as "dangerous and counterproductive" and said they are putting drivers "at risk" while causing an increase in pollution levels.
But Green MP Caroline Lucas said her party believes non-violent direct action is "legitimate when other forms of trying to raise issues with the government have failed".
Speaking to Sky News's Trevor Phillips On Sunday show, Ms Lucas highlighted how former UN general secretary Ban Ki-Moon has labelled climate issues an "emergency".
"In emergency situations we need to take emergency action and I believe that's what those protesters were doing," she added.
"It is a really difficult think to try to capture on a mild September Sunday, the fact that we are facing an existential threat to life on earth.
"That is a very odd thing to say over your breakfast but that is what we are facing.
"When it comes to the demands of those protestors, they want the government to insulate Britain and I cannot think of a more reasonable demand.
"It's a triple-win, it will get our fuel bills down, it would create thousands of jobs in every part of the country and it would get our climate emissions down too.
"Why has the government failed to do that?"
Ms Lucas described Insulate Britain's demands as "reasonable" and said it was "reasonable to take emergency action".
And, pressed on whether she believed blocking the M25 was a reasonable form of protest and whether she might join them, Ms Lucas replied: "I am saying that in extreme situations it is reasonable to take extreme actions and that is what has driven these protestors to do that.
"Personally, I prefer to take action where it is closer to the target of that action so that might be Downing Street, it might be the Treasury.
"But I fully understand why protestors have felt driven to do something more dramatic than that because government has been ignoring all of those kinds of actions for many, many years and we are facing an existential crisis and emergency and we need to take emergency action now."