London: Boris Johnson, the favourite to replace Theresa May as British prime minister, must appear in court over allegations he lied to the public about Brexit, a judge ruled on Wednesday.

The judge at London's Westminster Magistrates' Court ruled that Johnson, the former foreign secretary, must answer a private summons alleging he had committed three offences of misconduct in a public office.

Boris Johnson ahead of a nationwide bus tour to campaign for Brexit in May 2016. Credit:Bloomberg

These relate to claims that Johnson made in the run-up to and aftermath of the 2016 European Union referendum when he was one of the leading campaigners for Britain to leave the bloc. Britons voted by 52-48 per cent to leave.

"During both time periods outlined above, the (proposed) defendant repeatedly lied and misled the British public as to the cost of EU membership, expressly stating, endorsing or inferring that the cost of EU membership was £350 million ($640 million) per week," the application against Johnson says.