London’s Royal Opera House on Sunday condemned as “wholly inappropriate” the actions of a performer who held up a Palestinian flag onstage at the end of a performance.

Video footage posted online shows a brief scuffle at the edge of the stage as a figure dressed in a shirt and tie unsuccessfully attempts to stop the performer.

The incident in the British capital on Saturday during the curtain call came on the closing night of an 11-night run of Il Trovatore, a four-act opera by Giuseppe Verdi.

“Extraordinary scenes at the Royal Opera House tonight,” a person who claimed to have been in the audience posted on social media.

“During the curtain call for Il Trovatore one of the background artists came on stage waving a Palestine flag. Just stood there, no bowing or shouting. Someone offstage kept trying to take it off him. Incredible.”

A spokesperson for the Royal Ballet and Opera in London’s Covent Garden said the “display of the flag was an unauthorised action by the artist”.

The incident comes after numerous artists including Kneecap, Bob Vylan, Wolf Alice, and Amyl and The Sniffers offered messages of support for people in Gaza at this year’s Glastonbury festival.

Police are still investigating duo Bob Vylan, whose frontman led a chant against the Israeli army at the festival.

Kneecap’s Liam O’Hanna, known by his stage name Mo Chara, has also been charged with a “terror” offence over alleged support for banned organisations Hamas and Hezbollah in connection with an earlier performance.

Meanwhile, police arrested more than 100 people in London and other cities for supporting Palestine Action in a third consecutive weekend of protests over the government’s decision to ban the activist group using anti-terror laws.

Some 55 people were held at a demonstration in London’s Parliament Square under the Terrorism Act 2000 for displaying signs supporting Palestine Action, the Metropolitan Police said.

The protesters held up placards reading: “I oppose genocide. I support Palestine Action.”

Another nine were detained at a separate London march, and a further eight were held in Truro in Cornwall.

Other protests were held in northwestern Manchester where 16 people were detained, in western Bristol where another 17 were arrested, and in the Scottish capital Edinburgh, police said.

The rallies were organised by campaign group Defend Our Juries, which had said they were intended to “defy” the ban.

Since the Palestine Action ban kicked in on July 5, police have warned that expressing support for the group was now a crime, after a last-ditch High Court challenge failed to stop its proscription becoming law.

The government announced plans for the ban under the 2000 Terrorism Act days after activists from the group claimed to be behind a break-in at an air force base in southern England.

Two aircraft there were sprayed with red paint, causing an estimated £7 million (US$9.55 million) in damage.

Four people charged in relation to the incident remain in custody.

Palestine Action has condemned its – which makes it a criminal offence to belong to or support the group, punishable by up to 14 years in prison – as an attack on free speech.

The arrests come after 72 people were arrested at demonstrations across the UK last week and 29 the week before.