The 21-year-old climate campaigner was part of a demonstration near Mayfair's InterContinental Hotel on 17 October last year as oil executives gathered inside for a meeting.

Thunberg has now gone on trial at Westminster Magistrates' Court along with four other activists.

The court heard that on the day of the demonstration, protesters started to meet at the site at about 7.30am and police talked to the demonstrators about moving for better access for passers-by.

Prosecutor Luke Staton said a couple of protesters "were slowly abseiling down the side of the building" after gaining access to the roof just before 10.30am.

A section 14 condition was put in place at about 12.30pm, meaning the protest could continue but on the pavement to the south of the hotel.

It was said police found the move "necessary" to prevent disruption, as the "majority" of people inside the hotel could not leave and people could not get inside.

Mr Staton told the court that Swedish activist Thunberg was warned by one officer, before another officer "gave her a final warning".

"She said that she was staying where she was and so she was arrested," Mr Staton said.

Two Fossil Free London (FFL) protesters and two Greenpeace activists also appeared in court on Thursday for trial, after each pleaded not guilty in November to breaching the Public Order Act.

Environmental protesters demonstrated "in solidarity" with the defendants outside court on Thursday, holding up banners reading "climate protest is not a crime" and "who are the real criminals?".

Read more:
Thunberg pleads not guilty as she appears in London court
Thunberg joins protest against Farnborough Airport expansion

The other defendants were similarly informed of the section 14 condition and did not move to the designated protest area, the court heard.

Mr Staton said: "The Crown's case is that all five of these defendants took part in a public assembly.

"They knew or ought to have known that a section 14 condition had been imposed and they all failed to comply with that condition."

Thunberg made notes as proceedings went on.

The trial, which is expected to last two days, continues.