Scores of people had been arrested by early evening on the first day of Extinction Rebellion’s planned two-week shutdown of central London in protest against the lack of action to tackle the climate crisis.

Westminster Bridge, Lambeth Bridge, Trafalgar Square and Smithfield market as well as several roads in Westminster were blockaded by activists, with a focus on the areas around parliament in an attempt to force politicians to heed their warning.

The rate of arrests was significantly higher than when the group shut down central London for a fortnight in April. On that occasion police had detained 122 people by midnight on the first day.

Q&A What is Extinction Rebellion? Show Hide 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

The higher arrest tally reflected a more vigorous, speedier approach by police. Officers, including members of the territorial support group, swarmed the streets of Westminster early on Monday, stopping and searching people with rucksacks and big bags, as helicopters hovered overhead.

The 280 arrests by 9.30pm included at least two people in their 80s. Sarah Lasenby, an 81-year-old Quaker and retired social worker from Oxford, was detained outside the Ministry of Defence (MoD), and Phil Kingston, 83, was arrested at the Treasury for spray-painting in red the message: “Life, not death for my grandchildren.”

Haroon Siddique (@Haroon_Siddique) Phil Kingston, 83, was arrested during Extinction Rebellion protests for this graffiti on the Treasury pic.twitter.com/4qdiak2YHs

Highlighting the UK’s record of helping to finance fossil fuel development overseas, Kingston said after his arrest: “This represents complete disregard for the safety of the upcoming generation. I refuse to stand by and let that continue and will willingly accept imprisonment.”

Play Video 1:58 Extinction Rebellion protests launch around the world – video

Lasenby said: “The whole thing is so urgent that it is imperative the government should take serious actions and put pressure on other states and global powers to radically reduce the use of fossil fuels even if this means we need to reduce our comfort at home and so much flying.”

The protests began at 6.15am outside the MoD where activists attached themselves to cars before being removed by police using buzzsaws.

Facebook Twitter Pinterest Activists erect a mobile scaffold in Trafalgar Square. Photograph: Guy Smallman/Getty Images

Officers also used tools to remove a man who had attached himself to a tipi frame on Westminster Bridge. Others who were also forcibly removed included members of Extinction Rebellion’s youth movement, who had glued themselves to scaffolding in Trafalgar Square. As police took them down, the crowd chanted: “We are doing this for your children too.”

Others in Trafalgar Square attached themselves to a hearse with a coffin bearing the words: “Our future.”

By late afternoon police were blocking access to the protest on Millbank, which runs beside the Houses of Parliament and connects to Lambeth Bridge.

There was a carnival mood at many of the sites, with drummers playing outside Downing Street on Whitehall, where hundreds of people blocked the road, and a “rebel wedding” between two women on Lambeth Bridge.

As in April, relations between protesters and police were generally cordial, although arresting officers were met with chants of “Fuck you” on Westminster Bridge.

Facebook Twitter Pinterest Activists block Lambeth Bridge. Photograph: Henry Nicholls/Reuters

A 55-year-old woman from Brighton, who gave her name only as Venetia and was participating in the sit-in outside Downing Street, said: “It’s testament to the way they [the police] think we are an effective force that they think they have to intervene at that level. They’re pushing the boundaries of the law. I don’t blame individual officers but there’s a policy not to allow this kind of protest. But we still have a right to peaceful protest.”

Marie, 32, who did not wish to give her surname, was in Trafalgar Square at her first ever protest. She said she had been partly moved to attend because she works in fashion, which she said was one of the heaviest-polluting industries.

Facebook Twitter Pinterest The actor Mark Rylance takes part in the climate demonstration in central London. Photograph: Alastair Grant/AP

She said: “The atmosphere here is very nice, it’s people of all different ages and backgrounds. If you ask anyone what they want for their future they’d say they want a brighter future for their children. We need as many people as possible to have a voice. The system is not functioning. Infinite growth is a system and philosophy that needs to change. We consume too much.”

Extinction Rebellion activists are taking part in protests in cities around the world, including Sydney, Amsterdam, Berlin and New York.