Boris Johnson, the favorite 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 and ex-London mayor, must answer a private summons alleging he had committed three offences of misconduct in a public office.

These relate to claims that Johnson made in the run-up to and aftermath of the 2016 EU referendum when he was one of the leading campaigners for Britain to leave the bloc. 

"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 pounds ($442 million) per week," the application against Johnson said.

The 350 million figure was a central and controversial part of the pro-Leave campaign's "Take back control" message, famously emblazoned across a campaign bus. Opponents argued that it was deliberately misleading and it became symbolic of the divisions caused by the referendum.

In her written ruling, District Judge Margot Coleman said the allegations were not proven and she had made no finding of fact, but said Johnson should face trial.

"Having considered all the relevant factors I am satisfied that this is a proper case to issue the summons as requested for the three offences as drafted," Coleman said.