LONDON, United Kingdom - UK police on Wednesday charged Swedish climate campaigner Greta Thunberg with a public order offence, following her detention at a protest outside an annual gathering of energy industry figures in London.

The 20-year-old activist -- a key face of the movement to fight climate change -- was among 26 people charged by the capital's Metropolitan Police, after she was held at Tuesday's demonstration.

Thunberg was charged with "failing to comply with a condition" imposed under Britain's Public Order Act dealing with public assemblies and released on bail.

She is scheduled to appear at Westminster Magistrates' Court on 15 November.

Thunberg was on Tuesday taken away by two police officers and put into the back of a police van outside the Energy Intelligence Forum, after joining a mass protest there.

Several hundred protestors had gathered outside the InterContinental London Park Lane hotel during the "Oily Money Out" demonstration, organised by pressure groups Fossil Free London and Greenpeace, blocking all entrances to the venue.

Prior to her arrest, Thunberg criticised "closed door" agreements struck between politicians and representatives of the oil and gas industry.

London police said they imposed "conditions to prevent disruption to the public" after officers arrived at the protest, which were then breached and prompted the arrests.

"The protestors were asked to move from the road onto the pavement, which would enable them to continue with their demonstration without breaching the conditions," a police statement said.

Thunberg, who started the so-called "School Strike for Climate" movement as a teenager, was fined by a court in Sweden earlier this month.

It followed the court convicting her for having resisted arrest during a July protest that blocked traffic.