Police are seeking new legal powers against protesters after Extinction Rebellion demonstrators brought parts of London to a standstill.
The environmental campaign group is planning to shut down much of Westminster with rallies outside key buildings over two weeks of action starting on Monday.
The Metropolitan Police vowed to arrest an unlimited number of demonstrators if they break protest conditions, despite the “cost” to wider policing in the capital.
Assistant Commissioner Nick Ephgrave has written to the former policing minister, Nick Hurd, asking for a review of protest laws.
Speaking at a press briefing on Wednesday, he said the Home Office had pledged to consider the proposals including the creation of “banning orders” for protesters who repeatedly break the law.
Police also want the legal threshold for “serious disruption” to be changed, as well as sections of the Public Order Act that allow conditions to be imposed on protests and public assemblies.
“If we have people who are habitually protesting unlawfully, it would be helpful to have the ability of preventing them,” Mr Ephgrave said.
“The legislation around public order was drafted in a different era and it’s not particularly helpful because it wasn’t designed for what we’re dealing with now.”
Mr Ephgrave said more than 1,100 people were arrested at Extinction Rebellion’s protests in April, in a policing operation costing £16m.
Around 850 protesters have so far been prosecuted and 250 convicted.
“If you choose to come along to this protest and act unlawfully there will be consequences for you,” he said.
“We intend not just to arrest and detain, but if reasonable and proportionate we will prosecute.”
The senior officer denied the Metropolitan Police’s custody suites had been overwhelmed by the mass arrests and said he would not hesitate to detain the same amount of people again.
Questioned on whether the response was proportionate, he insisted the prosecutions were the “right thing to do”.
“Were we to allow unlawful protest to be tolerated it would encourage others to do the same sort of thing it’s difficult to see where that would end,” Mr Ephgrave said.
“It’s very dangerous if you start excluding certain types of protest from obeying the law.”
He acknowledged arrests may generate publicity for Extinction Rebellion, which has offered “arrestee support” training ahead of the new protests, but added: “It’s not our job to worry about their motivation, we just have to deal with the situation as we see it and try to get the balance right.”
Mr Ephgrave said the scale of the policing operation would have a “cost to communities in London”, as well as local businesses and police officers who are being put on 12-hour shifts.
“It’s undoubtedly the case that we will not necessarily be able to deliver a service to the level we would want to, right across London, during this two-week period,” he added.
“The same amount of work is going to have to be done by fewer people, working longer shifts with fewer breaks.
“That makes life much more difficult for our people. It means they might have to make compromises around which things they go to, how long they spend at incidents. I think communities may notice that.
“Whether it’s our ability to deal with street-based violence, whether it’s our ability to investigate things like domestic abuse, or any other crime you care to mention, there will be a cost.”
Frontline officers have been pulled off their normal shifts to tackle protests 83,000 times so far this financial year, compared to the 80,000 “abstracted” to respond to the 2017 London terror attacks and Grenfell Tower fire.
As well as using its own officers, Scotland Yard is to use “mutual aid” arrangements to drawn on specialists from other police forces, including those trained to remove demonstrators who attach themselves to roads and objects.
Following accusations Scotland Yard was too slow to react to Extinction Rebellion’s London protests in April, which saw the group block Waterloo Bridge and Piccadilly Circus, Mr Ephgrave said the force “wants to be ahead of what’s happening rather than responding to it”.
“We will police this within the law, fairly but firmly,” he added. “Our intention is that London stays open for business throughout this period and we will take whatever measures we can to make that happen.”
Mr Ephgrave said Extinction Rebellion had not been classified as an extremist group but would not confirm or deny whether police are spying on protesters using sources or undercover officers.
Officers have met with organisers of next week’s protests, which are planned for 12 locations in London including Trafalgar Square and outside Downing Street and the Department for Environment, Food and Rural Affairs.
Extinction Rebellion said former police officers had joined its protests and “many are prepared to risk their liberty to stand up for the planet”.
“We appeal to the humanity of the government and authorities to remember that we are non-violent protestors,” a spokesperson said.
“We appeal to their humanity to remember that we are facing an unprecedented global emergency. Many are losing their lives already and we are called upon as human beings to act now.”