The men stormed the Fabian Society conference in London moments after the mayor took to the stage and accused him of ‘subverting the English constitution’.
Mr Khan’s speech had to be suspended for several minutes as the demonstrators from a group called the White Pendragons were escorted out by police.
The chaos appeared to have been sparked by Mr Khan’s comments about the US President’s decision to cancel his UK visit.
Mr Trump claimed he pulled out of opening the new American embassy in London because he disagreed with the decision to sell off the old building for ‘peanuts’.
But Mr Khan said it was clear that Mr Trump had ‘got the message that many Londoners’ did not want him here.
As the London Mayor started to speak at today’s event, the protesters stood up and shouted that they were making a ‘citizen’s arrest’.
The men – who got into the event by buying tickets – also vowed to take the panel’s chair Kate Green MP into custody as well as Sir Keir Starmer and general secretary Andrew Harrop.
They then told guards that they were attempting to arrest the politicians under ‘common law jurisdiction’ and the Magna Carta – the 13th-century document that is often regarded as the foundation of the modern legal system.
As fellow demonstrators waved anti-EU signs and American flags, one of the group yelled: ‘Ladies and gentleman, we are here today to make a peaceful, non-violent citizens arrest of those being named.
‘They are Sadiq Khan, Keir Starmer, Kate Green MP and Andrew Harrop.
‘We stand under common law jurisdiction. If you touch us you will be done for common assault. Do not touch us. We’re not leaving, I’ve paid for a ticket.’
One of the protesters was English Defence League member Dave Russell, a self-described talk show host from London. He live-streamed the protest to his Facebook account racking up thousands of views.
Amid heckles and chants of ‘scum’, chair Kate Green MP told the audience: ‘I can assure you nobody is leaving and when the police arrive you will be able to talk to them.
’Those who would like to speak to the police can do so when they arrive. those who want to have a discussion about the future Labour government can stay in this hall.’
When he resumed his speech Mr Khan tried to make light of the incident with a reference to Prime Minister Theresa May’s Tory conference speech which was interrupted by a prankster, joking: ‘On the plus side I wasn’t served with a P45.’
And he also made another dig at the US president who described himself as a ‘very stable genius’.
Mr Khan said: ‘It is a pleasure to be here even though we were distracted by the actions of what some would call very stable geniuses.’