Boris Johnson has said that politicians who lie during political campaigns “should be made to go on their knees through the chamber of the House of Commons”.

To the audible amusement of some in the audience, the prime minister was asked during Friday’s BBC leaders debate what the punishment should be for politicians who tell deceive the public in order to further their own agenda.

“Well, they should be made to go on their knees through the chamber of the House of Commons, scourging themselves with copies of their offending documents which claim to prove one thing and actually prove something quite different,” Mr Johnson replied.

It is the second time the prime minister has prompted laughter while facing questions over trust in politics during the general election campaign, of which questions over his own personal integrity has been a central issue.

His prior “die in ditch” Brexit pledge, his promise of £350m for the NHS during the 2016 referendum campaign, and the number of children he has fathered have all been weaponised by his opponents.

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As well as Game of Thrones-esque humiliation, Mr Johnson’s response on Friday included a clear dig at Labour’s claims that a 451-page dossier of transcripts of Whitehall meetings with US trade officials contains proof of a Tory plot to “sell off the NHS”.

The Uxbridge and South Ruislip candidate was challenged throughout the debate over the documents, which show US negotiators pushed for “full market access” to services, including the NHS, and to extend patents on drugs held by American corporations to the UK in a way that would increase drug prices.

The prime minister, who as a nascent MP voiced public opposition to the “monolithic, monopolistic” NHS, mocked the opposition’s accusations as “Bermuda triangle stuff”, joking: “We’ll be hearing about ‘little green men’ next.”

He added: “Under no circumstances will we sell it off to anybody in any kind of trade deal.”

A snap Yougov poll after the debate found just 35 per cent of people thought Mr Johnson had performed better than his rival on the NHS, compared to 55 per cent who believed Jeremy Corbyn had.