The London mayor has demanded the state response to Just Stop Oil remain “within the law”, as civil rights campaigners warned over the prime minister’s suggestion he would grant police new powers to contain the group’s protests. After a meeting of police leaders and ministers in Downing Street on Thursday, Rishi Sunak promised police whatever powers they need to “clamp down” on the “completely unacceptable” disruptions by the climate activist group. Since April, Just Stop Oil has been waging a campaign of direct action protests, and vowed not to stop until the government agrees to ban all new fossil fuel projects in the UK. On Friday, Sadiq Khan said he worried that some of Just Stop Oil’s tactics, which have included trespassing on oil terminals, blocking motorway traffic and targeting works of art, were “driving people away from joining the campaign to tackle the climate emergency”. But speaking during a visit to a homeless charity in south London, the mayor added: “What the government has got to realise, though, is that protest is a cornerstone of our democracy, and they have got to make sure they take action within the law.” Khan’s concerns were echoed by others in London’s local government. Green London Assembly member Caroline Russell said: “The freedom to protest is a human right. The police, crime, sentencing and courts bill already gives police the power to treat peaceful protesters as criminals. “It is shocking that the prime minister is suggesting extending powers that would crush democratic freedoms and stifle the right to protest, especially following reports of officers abusing their powers with protesters in the past.” Khan’s intervention comes after police hailed a “constructive” meeting with Sunak, the home secretary, Suella Braverman, and the policing minister, Chris Philp, at No 10, called at the PM’s request in response to Just Stop Oil’s protests. Asked after the meeting about new legislation to boost police powers, Sunak said: “We are currently giving the police new powers so that they can clamp down on these illegal protests. “They will have my full support in acting decisively and rapidly to end the misery and the disruption that’s being caused to ordinary families up and down the country. I’ve said to the police whatever they need from government they will have in terms of new powers.” Jodie Beck, the policy and campaigns officer at the human rights organisation Liberty, said campaigners were “deeply concerned” by the promise. “The government are already pushing through the public order bill, just months after handing out sweeping powers to police in the Police, Crime, Sentencing and Courts Act which have been used to create a hostile environment for protesters,” she said. “The powers of the police are already so broad that they will always be open to abuse, and have recently led to situations including journalists being arrested for simply covering protests. “Creating more protest-specific police powers will have a chilling effect on the right to protest, at a time when existing measures have already created an increasingly hostile environment for campaigners. More police powers are not the answer and show we are heading in the wrong direction.” Police have already been accused of overreach after four journalists were arrested while covering Just Stop Oil’s M25 actions, prompting accusations of threats to press freedom. A subsequent investigation by another force found the arrests were potentially unlawful. Just Stop Oil has repeatedly said it will not be deterred by stiff sentences or enhanced police powers. November’s actions on the M25 led at one point to the jailing of more than three dozen of the campaign’s supporters, mostly on remand. On Tuesday, Jan Goodey was jailed for six months after admitting causing a public nuisance for causing “mile after mile” of tailbacks on the M25. “If Rishi Sunak was serious about stopping this disruption, instead of wasting police time he would crack on with ending new oil and gas now,” Just Stop Oil said. “It’s climate chaos that threatens social stability and the rule of law, not climate action.” Just Stop Oil returned to London’s streets at the start of the week with a new protest tactic: walking slowly on busy high roads to obstruct traffic during rush hour. Speaking to the London assembly’s police and crime committee on Thursday, the Met commissioner, Sir Mark Rowley, said the “less assertive” protests reflected “a large number of their leaders being remanded in custody as a result of our operations”. The new tactic makes any clampdown more difficult, however. Referring to the protests, Matt Twist, an assistant commissioner at the Met, said it was “frustrating for Londoners seeing them walking slowly in the roads”. He added: “But as they have been small in number, and keep moving with traffic being able to move around them or easily divert, we are less likely to be able to arrest and prosecute them for unlawful obstruction.”