Pro-Trump protesters have tried to arrest the Mayor of London Sadiq Khan, after Mr Khan said the US President wasn't welcome in the British capital.
Mr Khan was speaking on gender equality at a conference when members of far-right group the White Pendragons interrupted, British media reported.
"Ladies and gentlemen, we're here today to make a non-violent, peaceful citizen's arrest," one man told the crowd, who booed and heckled the group.
Several police soon removed the pro-Brexit protesters, who denied they were racist.
"They told us Sadiq Khan has no right to be Mayor of London, referencing his religion," ITV reporter Paul Brand tweeted after speaking with some of the men.
"It is a pleasure to be here even though we were distracted by the actions of what some would call very stable geniuses," Mr Khan said once he was able to resume speaking, referencing a recent tweet by Mr Trump calling himself a "very stable genius".
Mr Khan said "Londoners have made it clear that Donald Trump is not welcome here" following the President's recent comments about "shithole" countries.
Mr Trump was scheduled to travel to London to open a new embassy, but he cancelled.