Climate activists have caused serious disruption to rush-hour traffic in London with a series of “swarming” roadblocks at several different locations around the capital as police warned motorists that more protests were expected.

From 8am on Wednesday groups of protesters coordinated by the group Extinction Rebellion walked on to roads in Westminster, Tower Bridge, Elephant and Castle, and Earl’s Court, blocking traffic for several minutes at a time in a plan to bring gridlock to the city.

The Metropolitan police said that protests could continue until Saturday and advised against driving into the city. The Met also warned people that attempting to drive through the demonstrations was “very dangerous and illegal”.

Roads&Transport MPS (@MPSRTPC) On the 22-24 Nov, there will be protests across London that may result in delays to your journey. We advise not to travel by car or motorbike. If you do drive into London please note attempting to drive through protestors in the road is very dangerous and illegal

A spokesperson for Transport for London said Wednesday’s protests had caused serious disruption to traffic and buses. The action was met by an ambivalent response from some members of the public on their way to work, but others said they backed the demonstrations.

Facebook Twitter Pinterest Climate protesters from the Extinction Rebellion group hold placards and banners as they block traffic in Elephant and Castle. Photograph: Jack Taylor/Getty Images

The protests are part of a campaign of mass civil disobedience organised by Extinction Rebellion, which wants to force governments to treat the threats of climate change and species extinction as a crisis.

As traffic began to back up around London, the group sent a letter to the business secretary, Greg Clark, outlining their demands. “We are writing to let you know that we intend to continue our support for rebellion against the UK government,” their letter said.

“We would like to meet with you at your earliest convenience to work out ways in which you can exercise your responsibility as secretary of state to protect the ecosystems and people of this country.”

Facebook Twitter Pinterest Environmentalists bring traffic to a standstill across the capital. Photograph: Jack Taylor/Getty Images

Ronan McNern, a protest organiser and a signatory to the letter, said the plan was to cause as much disruption as possible with the smallest numbers.

“The lights go red, they go into and sit down in the road, wait seven minutes,” he said. “If anybody needs to get past, we’ll let them through. Come off after seven minutes, take a break, let the angry drivers at the front go, then the light goes red and you go on again.

“This is about causing economic disruption by slowing things down, bringing things to a gridlock. This is an experiment, really. I think that’s the most important word.”

The Guardian met one group of about 35 protesters by the statue of Nelson Mandela at Parliament Square at 7am, then followed the group as they walked to the south end of Lambeth Bridge, the site of one of central London’s busiest junctions.

Just before 8am they walked out into the road, chanting and carrying banners and placards. Traffic was soon backed up far down Albert Embankment, Lambeth Palace Road and Lambeth Road, as motorists found the way over the Thames blocked.

Cars sounded their horns and one driver got out to remonstrate with police monitoring the protesters. Officers told him to be patient. Another passerby, who asked police why they could not clear the roadblock, was told the activists had a right to protest. “You’re part of the problem and all,” he shouted back at them.

Demonstrators then moved on to Vauxhall Bridge and then Victoria Street, where they continued their rolling blockades. They allowed cyclists and emergency vehicles with blue lights to go past.

At one point the comedian Jim Davidson became caught up in the demonstration and got out of his car to remonstrate with police for not forcing the protesters to move.

Tom Edwards (@BBCTomEdwards) Jim Davidson was stuck at the front - got out of his car shouted at the Police “Why aren’t you moving them?” - when a protestor tried to talk to him he said he didn’t talk to lefties. One gag: “Climate change ? Don’t they like being warmer!!” . pic.twitter.com/tOyNikdcvG

James Page, 46, a decorator who stopped to watch a blockade close to Victoria, said he “couldn’t give a damn” about climate change. “It [the climate] all balances out,” he said. “It’s shown from time it balances itself out. It’s not something I would be bothered about anyway.”

At Elephant and Castle, a major junction linking south London to the City financial district, protesters’ numbers were bolstered after lunch by the arrival of several dozen students from the nearby London College of Communication.

Damien Gayle (@damiengayle) With the #extinctionrebellion #Swarming protest in Elephant and Castle now, where numbers have been bolstered by students from South Bank Uni pic.twitter.com/Y0ZlmJJhb9

One student, Renee, 18, who declined to give her surname, said the protest was “incredibly impactful”.

“It’s supporting issues that are very prevalent nowadays that people should know about. I don’t know if it’s the right way to do protest, but at the end of the day it has an effect.”

Her friend, Ekene, 18, worried that the methods might alienate people, “so then obviously when they see the cause, they are going to associate it with anger. So I’m not sure if it’s the best way.” Nonetheless, both said they would join the next Extinction Rebellion protest, planned for Saturday.

Damien Gayle (@damiengayle) "I don't know if it's the best way to do protest, but at the end of the day it has an effect."



Ekene, left, and Renee, right, students at London College of Communication, say they will attend #ExtinctionRebellion's next big protest on Saturday after #Swarming in Elephant pic.twitter.com/iQCB7MhvjZ

Dr Larch Maxey, who was helping to coordinate the Elephant and Castle protest, said: “These students have just heard about it and jumped in, and this is what our movement is doing.

“I’ve been on marches for decades about this. We’ve had massive marches and they’ve just been ignored. But you cannot ignore people shutting down the city.”

As in Westminster, police facilitated the protest and tried to assuage the anger of motorists.

Facebook Twitter Pinterest Demonstrators also occupied London bridges during an earlier protest on 17 November. Photograph: Xinhua/Barcroft Images

Howard Rees, an organiser, said the actions had been a success. “Quite a lot of extra people have joined over the course of the day, because they’ve seen what’s going on on social media. We’ve got more people on board, and hopefully they will come along tomorrow.”

A spokesperson for Transport for London initially said there had been significant disruption during rush hour, but later retreated from that assessment.

“The demonstrators were blocking traffic, causing delays to roads and buses in the areas of protest,” the spokesperson said. “The delays are now clearing.”

McNern added: “Three weeks ago no one knew the name Extinction Rebellion, then there was the declaration [of rebellion], there was the week of action, there was 6,000 people [on the bridges through central London on Saturday].”

On Saturday, 82 protesters were arrested after occupying Southwark, Blackfriars, Waterloo, Westminster and Lambeth bridges, in one of the biggest acts of peaceful civil disobedience seen in the UK in decades.

In the previous two weeks, police arrested more than 60 activists for taking part in acts of civil disobedience, ranging from gluing themselves to government buildings to blocking roads. Many activists were arrested more than once.

McNern said all the activists were willing to be arrested. “So it’s very different from when you are dealing with people who are scared of being arrested.”

He said the group had told the police of their plans and they were willing to abandon any blockade that hampered the movement of emergency vehicles.

Organisers say they hope the campaign of “respectful disruption” will change the debate around climate change and signal to those in power that the present course of action will lead to disaster.