A man allegedly captured on video at the far-right rally in London on Saturday threatening to kill Keir Starmer has been arrested by police.

An investigation was launched on Sunday in connection with the video, which was filmed at the event organised by the far-right activist Stephen Yaxley-Lennon, known as Tommy Robinson.

The footage included an interview with a man who said that “Keir Starmer needs to be assassinated” and “someone needs to shoot Keir Starmer”. Metropolitan police had said it was aware of the video, which was circulating on social media, and was attempting to identify the man.

A spokesperson for the Met said: “A man has been arrested in relation to a video referencing Sir Keir Starmer which was filmed during the ‘unite the kingdom’ protest on Saturday 13 September in central London.

“On Sunday 14 September police arrested a 56-year-old man on suspicion of malicious communications. He was taken into custody and later released on bail pending further inquiries.”

Scotland Yard estimated that at least 110,000 people attended the event. A total of 26 police officers were injured in clashes as projectiles were hurled, and the Met said on Sunday that 24 people had been arrested for a range of alleged offences including common assault and violent disorder.

The force said a post-event investigation was under way, with officers working to identify other people involved in disorder with a view to making further arrests.

Speakers included the owner of Tesla and X, Elon Musk, who was condemned by Downing Street for using “dangerous and inflammatory” language at the event. The billionaire, who appeared via a live link, told a crowd of protesters that “violence is coming” and “you either fight back or you die”.

Marchers had travelled to London by train and coach for a demonstration, which was billed as a “festival of free speech”, but by its conclusion had amplified racist conspiracy theories and anti-Muslim hate speech across Whitehall.

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The scale of the protest vastly outgrew police estimates, resulting in tense and at times violent clashes between protesters and police.