Climate change activists aiming to “shut down London” have entered their third day of protests.
Extinction Rebellion protesters have been blocking traffic at Marble Arch, Waterloo Bridge, Parliament Square and Oxford Circus since Monday.
Almost 300 people have so far been arrested. The Met Police said “contingency plans are in place should custody suites become full”.
Campaigners said they planned to target the Tube network on Wednesday.
British Transport Police said extra officers would be on duty throughout the day.
Supt Matt Allingham added: “We will not tolerate any activity which disrupts the millions of passengers who rely on using the rail network in London.”
Extinction Rebellion said the non-violent disruption was to “highlight the emergency of ecological collapse” and persuade ministers to meet group members.
It added: “Participants will peacefully break the law in order to stop the Tube and then will wait to be arrested.
“We sincerely apologise to all those who may suffer as a consequence of this disruption. In any other circumstances we would never dream of disrupting the Tube but this is an emergency.”
Protester and climate lawyer Farhana Yamin, who was arrested on Tuesday, told BBC Radio 4’s Today: “I totally want to apologise to people using public transport.
“But at the same time we need to take actions that are disruptive so everyone understands the dangers we’re facing right now. People should understand that we are at a critical moment in our humanity’s history.”
London Mayor Sadiq Khan urged protesters to “think again” about disrupting Tube services which could “risk Londoners’ safety”.
In a statement posted on Twitter he added: “It is absolutely crucial to get more people using public transport, as well as walking and cycling, if we are to tackle this climate emergency – and millions of Londoners depend on the Underground network to get about their daily lives in our city.”
Jace Tyrrell, chief executive of the New West End Company, said the first two days of protests had so far caused a loss of £12m in trade in the West End.
He told BBC Radio London: “Everyone has a right to peaceful protest… But this is really disruptive for us.”
In Edinburgh, dozens of people were arrested when hundreds of protesters blocked a main road.
Organisers said protests had been held in more than 80 cities across 33 countries and wanted to continue “shutting down London” until 29 April.
Campaigners at Waterloo Bridge and Oxford Circus have been ordered to restrict their protests to Marble Arch after they caused widespread disruption on Monday. That order will continue until 21:10 on Friday.
Joao Verga, who works at a printing company, says the protesters at Oxford Circus have caused him disruption.
The 58-year-old said: “We’re trying to make a living and we can’t. We move very quick in this country, this is only going to slow down everything.”
Three men and two women, in their 40s and 50s, arrested on suspicion of criminal damage at Shell’s headquarters in London on Monday, have since been released while inquiries continue.
The majority of the other protesters detained have been held on suspicion of public order offences.
What is Extinction Rebellion?
Since the group was set up last year, members have shut bridges, poured buckets of fake blood outside Downing Street, blockaded the BBC and stripped semi-naked in Parliament.
It has three core demands: for the government to “tell the truth about climate change”, reduce carbon emissions to zero by 2025, and create a citizens’ assembly to oversee progress.
Controversially, the group is trying to get as many people arrested as possible.
But critics say they cause unnecessary disruption and waste police time when forces are already overstretched.
The government said it shared “people’s passion” to combat climate change and “protect our planet for future generations”.
The Department for Business, Energy and Industrial Strategy said the UK had cut its emissions by 44% since 1990.
A spokesman said: “We’ve asked our independent climate experts for advice on a net zero emissions target and set out plans to transition to low emission vehicles and significantly reduce pollution through our Clean Air Strategy.”