The “historic” march in favour of a second Brexit referendum was attended by just a third of the number that its organisers claimed, according to an official estimate.

A debriefing document prepared by the Greater London Authority put the number of attendees at October's People’s Vote rally at 250,000 - significantly below the campaign group's claim that they were joined by more than 700,000 people.

Last night the group was accused of attempting to mislead politicians and voters about its level of support.

Anne-Marie Trevelyan, the Conservative MP for Berwick-upon-Tweed, said: “Leaving the EU was an option on the ballot paper that attracted more votes than any referendum or politician in our history.

"The People’s Vote would do well to remember this and should stop attempting to dupe people about how many people support it."

But the People's Vote campaign insisted its estimates were "based on intelligence from both volunteers and professional stewards" and took account of the numbers that joined the march from the front, while it was in progress, which it suggested could have been discounted by other calculations.

The People's Vote website states: "On October 20th, over 700,000 people marched from Park Lane to Parliament, demanding their future back."