Police have accused Extinction Rebellion of causing “high level” disruption and called for courts to pass sentences big enough to deter them from causing fresh chaos, as the environmental group braces itself for mass prosecutions of its activists.

Laurence Taylor, the deputy assistant commissioner in charge of protest policing for the Metropolitan force, said last April’s mass civil disobedience, when thousands of activists occupied four sites across London, saw 90 of the people being arrested only to be released and rejoin the protests. Taylor said police were talking to the government about tougher and clearer powers.

“We would like to see, where behaviour crosses those thresholds of criminality, where we have to react and use powers to deal with it, that the type of sentencing that you might receive would, as it does for other offences, act as a deterrent,” Taylor said.

Legal teams representing those Extinction Rebellion supporters arrested so far said they now expect almost all of the 1,100 people detained during the civil disobedience protests in the spring to be taken to court – with 50 of them due before Westminster magistrates on Friday.

Q&A What is Extinction Rebellion? Show Extinction Rebellion is a protest group that uses non-violent civil disobedience to campaign on environmental issues. Launched in October 2018, with an assembly at Parliament Square to announce a 'declaration of rebellion' against the UK Government, the group has staged regular demonstrations against current environmental policies. More than 1,000 activists were arrested in April 2019 after protesters occupied four sites across London, as well as blocking roads, disrupting a railway line and conducting a protest at Heathrow. Other demonstrations have included a semi-naked protest inside the House of Commons and blockading streets in London, Cardiff, Leeds, Bristol and Glasgow. The group says climate breakdown threatens all life on Earth, and so it is rebelling against politicians who “have failed us”, to provoke radical change that will stave off a climate emergency. The movement has become global with groups set up in countries include the US, Spain, Australia, South Africa and India. Martin Belam Photograph: Anadolu Agency/Anadolu

Mike Schwartz of Bindmans, one of the defence lawyers involved, said the move by the police and the CPS appeared to be “a deliberate and expensive” attempt to “browbeat those in society most motivated to do all they can, peacefully but firmly, to mitigate environmental collapse”.

To date, 180 people have been charged and police have promised to be more robust to limit further disruption.

“This is an extraordinary decision at a time of austerity, a creaking criminal justice system, rising knife crime and falling rape prosecutions,” said Schwartz. “The proportionality and altruism of the community’s actions is in stark contrast to the face-saving short-termism of the authorities.”

Taylor revealed that his force this week went hunting for a boat that Extinction Rebellion wanted to use, to make sure it could not be secured to a location and cause more disruption.

He said police have to balance the rights of everyone, and their views, including those of media commentators: “With public order policing, there are fine balances between what is acceptable to the wider public, what is acceptable to high-profile people in the media, what the commentary will be around that, and also what the protest groups want to achieve.”

He said the new form of protest, which can last for long periods, drained resources from frontline policing, in part because its peaceful nature could mean four officers are needed to lift up and carry away someone blocking a road: “These protesters are quite unique because [they] are by and large peaceful,” he said.

“It is almost easier to deal with people who are being violent towards you, because you can use a level of force commensurate with that.”

The protests earlier this year are claimed to have cost £16m but the bill will be higher if investigating those arrested, and court costs, are included.

Taylor said: “It is not acceptable to bring London to a standstill. It is not acceptable to close major routes in London, and build barricades and put obstacles into the road and secure them there that make it very, very difficult for us to move.”

Taylor vowed there would be no repeat of the scale of April’s disruption and said Extinction Rebellion’s planned next mass action in October would stretch police at a time when they are expecting a series of demonstrations linked to Britain’s potential exit from the EU.

He added it was not the Met’s job to be the “moral police” and adjudicate on the rightness or otherwise of protesters’ causes.

The crackdown by the authorities comes amid a new wave of Extinction Rebellion protests this week, which have seen people take to the streets in London, Leeds, Bristol, Cardiff and Glasgow as they demand urgent action to tackle the climate crisis.

In Bristol, protesters were arrested after they blocked a main road that leads to the M32 motorway. In London, protesters blocked the gates of a concrete factory and gathered outside the Greater London Authority to urge people to withhold a proportion of their council tax “to demand action, not rhetoric”.

The latest wave of protests came as the Met police confirmed it was “continuing to progress” more than 900 cases from the April demonstrations and was working closely with the Crown Prosecution Service.

Extinction Rebellion said it welcomed this “extraordinary opportunity” to take its message into the courts, which would give its “rebels a platform to speak the truth about the dire situation we’re in”.

“Our legal team also hopes to use these cases to set a major precedent in British law, establishing a citizen’s right to act in the face of emergency,” a spokesperson added.

But it questioned the motivation behind the prosecutions, saying police had taken a relatively hands-off approach to the protests at the time, but that subsequent criticism of the Met appears to have stung.

“The burden this tsunami of cases will place on the courts is unprecedented and will impact the day-to-day work of the criminal justice system,” said the spokesperson. “With most defendants likely to receive a conditional discharge, the waste of court time and resource is unjustifiable.”

A spokesperson for the CPS said: “The CPS is a demand-led organisation and we must review each case referred to us by the police. The role of the CPS is to decide whether there is sufficient evidence to prosecute and if it is in the public interest to do so on the merits of each case.”