Four climate activists on hunger strike have pledged to continue going without food for a second week as they call on political leaders to act on the environmental crisis.

More than 520 people in 28 countries, from Barcelona to Stockholm, joined Extinction Rebellion’s global hunger strike a week ago.

Most of them – including at least 260 in the UK – signed up to go without food for seven days, but four of those in London say they intend to continue.

In the UK, protesters camped outside the headquarters of the main political parties, including 83-year-old Ursula Pethick.

Extinction Rebellion campaigners have asked all parties for a filmed meeting. The Conservatives and the Brexit Party are the only ones not to have responded, the group claims.

Brexit and climate protests at Labour party conference: In pictures Show all 12 1 /12 Brexit and climate protests at Labour party conference: In pictures Brexit and climate protests at Labour party conference: In pictures Labour leader Jeremy Corbyn walks past anti-Brexit campaigner on the second day of the party conference in Brighton AFP/Getty Brexit and climate protests at Labour party conference: In pictures A protester holds a sign mocking Labour leader Jeremy Corbyn's Brexit stance at the party conference in Brighton EPA Brexit and climate protests at Labour party conference: In pictures Activists from anti-climate change movement Extinction Rebellion march on the Labour conference in Brighton AFP/Getty Brexit and climate protests at Labour party conference: In pictures Delegates take part in an informal vote on Labour's Brexitr stance at the party conference in Brighton AFP/Getty Brexit and climate protests at Labour party conference: In pictures Shadow foreign secretary Emily Thornberry leads a march in support of a second referendum on Brexit Getty Brexit and climate protests at Labour party conference: In pictures Anti-Brexit protesters take part in a People's Vote rally during the Labour party conference in Brighton EPA Brexit and climate protests at Labour party conference: In pictures Extinction RebelliActivists from anti-climate change movement Extinction Rebellion march on the Labour conference in Brightonon EPA Brexit and climate protests at Labour party conference: In pictures Extinction Rebellion activists march on the Labour conference in Brighton AFP/Getty Brexit and climate protests at Labour party conference: In pictures A delegate arrives carrying a briefing from the Labour Representation Committee to the Labour party conference in Brighton Getty Brexit and climate protests at Labour party conference: In pictures Prominent anti-Brexit campaigner Steve Bray protests on Brighton beach during the Labour party conference Reuters Brexit and climate protests at Labour party conference: In pictures Anti-Brexit protesters take part in a People's Vote rally during the Labour party conference in Brighton EPA Brexit and climate protests at Labour party conference: In pictures Activists raise a banner calling for the Labour party to restore the original Clause 4 of its constitution, which would pledge the party to nationalising all industry Getty

The Lib Dems, Greens and Plaid Cymru have agreed to meetings, and the group is in discussions with Labour about holding one, members said.

Boris Johnson did not reply to campaigners camped outside his party’s base who called out to him to ask to meet on Saturday, merely giving a wave as he left the building to get into an official car, video on Twitter suggested.

In Israel one protester has been on hunger strike for more than two weeks.

After five days, another hunger striker, Steven Hollies, tweeted: “I am noticeably more lethargic this morning. I feel thin and hollow.” And by day six he added he was even more tired.

Members said the aim of the hunger strike was to highlight the vulnerability of food security caused by the climate crisis.

“People are already starving due to #ClimateBreakdown, and food insecurities will hit the UK too,” the group said.

Mike Goldthorn, 30, a care worker from north Wales, said: “We are hunger-striking in solidarity with the people already suffering and the generations to come.

“I’ve been on hunger strike since Monday and people I’ve been chatting to are amazingly supportive of what we are doing.”

Emma Taylor, a prospective Labour candidate for Heene in West Sussex in next May’s elections, said: “Three decades of protests, petitions and campaigns have failed to secure an emergency response to mitigate ecological and climate breakdown. Drastic times call for drastic measures.”

A Brexit Party spokesman said Extinction Rebellion had claimed to have given a letter personally to Nigel Farage, the party leader, but that officials were not aware of it, adding that Extinction Rebellion members had turned up at the manifesto launch.

“We would encourage them to write in, like other political groups, and go about things in a normal, civilised way, rather than this unusual means,” he said.

The manifesto included an extensive section on environmental policies, he added.