Greta Thunberg has joined protesters at a “climate justice memorial” in the City of London to protest against the financing of fossil fuel industries ahead of the Cop26 summit.

Activists from environmental groups including Pacific Climate Warriors, Coal Action Network and Extinction Rebellion laid wreaths and flowers at the entrance of the Lloyd’s headquarters.

The Swedish climate campaigner joined activists outside Standard Chartered chanting: “We are unstoppable, another world is possible” and: “What do we want? Climate justice. When do we want it? Now.”

Thunberg also said she had “not officially” been invited to Cop26. In a preview clip for an interview with Andrew Marr for his BBC One show, she said: “I don’t know. It’s very unclear. Not officially … I think that many people might be scared that if they invite too many radical young people, then that might make them look bad.”

When asked by Marr whether more young people should have been invited to attend the climate convention, she said: “Not necessarily radical young voices, but we need more representation from the so-called global south, from the most affected people and areas.

“It’s not fair, when for example one country sends lots and lots of delegates, and then another country is very under-represented. That already creates an imbalance and climate justice is at the very heart of this crisis. As long as we keep ignoring the historical responsibility of the countries of the global north and as long as we continue to ignore it, the negotiations will not have a successful outcome.”

Friday’s demonstrations were part of global action targeting the financial centres of the largest economies around the world the weekend before the UN’s Cop26 climate summit. Activists aim to draw attention to the disadvantaged communities most affected by the climate crisis in what they hope will be the largest financial climate protest in history.

“We want to commemorate and commiserate the homes and lives lost to the climate crisis,” one Extinction Rebellion member said on Friday.

“We want to call on Lloyd’s as Pacific Islanders to move the money away from fossil fuel industry so we can put an end to an era which is exporting harm directly to our islands,” said Brianna Fruean, who came to the UK to participate in Cop26.

Lloyd’s is an insurance market which Coal Action Network, one of the protest’s organisers, claims “underwrites the majority of the world’s most climate-wrecking projects”.

The demonstrations have also targeted Macquarie Group, an investment bank that the protesters have said is financing the Silvertown tunnel in London, which is planned to link the borough of Newham and the Greenwich peninsula. Extinction Rebellion activists say the tunnel will bring more traffic and pollution to Newham, which is one of the city’s most deprived and polluted boroughs, though the mayor’s office has said it does not expect it to worsen pollution.

Protests took place in 26 countries on Friday, and are also targeting JP Morgan Chase in the US and Deutsche Bank in Germany.