Thousands of students and activists have taken to the streets of more than 50 British towns and cities demanding urgent action on climate change for the third time in as many months.

The organisers of the Youth Strike 4 Climate movement said “sizeable events” took place in London, Sheffield, Manchester and Brighton, among other towns and cities. They mirrored events around the world, as protesters from cities as far apart as Helsinki and Delhi took to the streets.

In London, protesters walked across Westminster Bridge waving banners demanding a “Green New Deal”, before bringing Oxford Street to a halt by sitting down in the middle of the famous shopping thoroughfare.

Drivers looked out of their car windows, irked as young people banged on their doors, telling them to turn their engines off. Bus drivers sat in traffic on gridlocked streets, their vehicles devoid of passengers.

George Bond, 16, one of the organisers of the youth climate strike said that they decided to disrupt London’s busy shopping district because of the link between consumerist culture and climate change.

“It’s a stark reminder that in the western world we enjoy a culture of convenience, while people in the global south are working in bad conditions and suffering the most from climate change,” he said.

The Metropolitan police said there had been no arrests, though one student was taken into a police van for refusing to move.

Earlier, between 400 and 800 students joined a range of youth and leftwing activist groups in Parliament Square. Theo Sharieff, 23, a Socialist Students organiser from Birmingham, said: “To fight climate change we need socialist change.”

Creative banners abounded. One youngster held a poster with teenage actor Timothee Chalamet which read “the Earth is getting hotter than Timothee Chalamet”. An eight-year-old, Agnes Freij from St Aidan’s primary school held a banner with a painting of Dr Zeus’ Lorax reading: “I am the Lorax and I speak for the trees.”

She told the Guardian: “The Lorax speaks for the trees because they don’t have mouths. Right now I think the trees would be saying, stop this climate crisis.”

In the Highlands, Holly Gillibrand, who has gained national prominence for her activism, was on strike for the 14th week in a row, in her usual spot outside her school in Fort William with friends. Gillibrand, 13, was not missing school because the Easter break is under way in Scotland.

Young climate change protesters make their point in central London. Photograph: Martin Godwin/The Guardian

She said: “I think it’s important to strike during the holidays because people were saying that we were on strike because we got to miss school. This shows were are dedicated and willing to give up our free time for this crisis.”

Gillibrand has met Scotland’s first minister, Nicola Sturgeon, and wants to see politicians take more action. “We’re a rich, developed country so we need to be reducing our emissions more quickly,” she said.

In Sheffield, the former Green party leader Natalie Bennett was among the speakers at a city centre rally.

At the end of the London march, a selection of letters were read out by activists at Oxford Circus, including submissions from Yoko Ono, Kate Tempest and Rebecca Solnit.

More than 15,000 students took part in the first Youth Strike 4 Climate event in February, which organisers said was prompted by the alarming inaction of the government. Precise figures for Friday’s turnout were not immediately available – but some found it easier to attend as some schools are already on their Easter break.

Jake Woodier, of the UK Student Climate Network, said: “Thousands upon thousands of young people across the UK have shown their resolve by continuing to demonstrate for climate justice for the third month in a row, while also demanding a Green New Deal for the UK.

“This idea is by the people, for the people and puts people and the planet on an equal footing. The time for action is now.”

The youth climate movement was inspired by the Swedish schoolgirl Greta Thunberg, 16, who has gone on strike every Friday since August 2018. Thunberg is currently in her 34th week of striking outside the Riksdag parliament building in Stockholm.

The latest strikes come after a UN report warned that limiting temperature increases to 1.5C above pre-industrial levels – the point beyond which climate impacts become irreversibly severe – needs new levels of action.

On Thursday, the environmentalist and broadcaster David Attenborough told the IMF spring meeting that humans have at most 20 years to prevent the complete destruction of the environment.

The Norwich South MP Clive Lewis signalled the Labour party’s support for the movement, writing: “The time for incrementalism has passed. The young people striking today recognise this.”

The environment secretary, Michael Gove, has expressed support for the strikes, saying collective action can make a “profound difference”.