LONDON • Mr Boris Johnson, the front runner to become Britain's next prime minister, must attend court over allegations that he knowingly lied during the Brexit referendum campaign, a judge announced yesterday.

Mr Johnson, the former foreign secretary, will be summoned to appear before a court over allegations of misconduct in public office, Judge Margot Coleman said in a written decision, without specifying the date.

The case is over the claim that Britain sends £350 million (S$611.5 million) a week to the European Union. The exact amount of Britain's net and gross EU contributions was one of the biggest issues during the 2016 referendum campaign.

Businessman Marcus Ball has crowdfunded the private prosecution against Mr Johnson.

Judge Coleman's decision follows a hearing last week at Westminster Magistrates Court in London. "The allegations which have been made are unproven accusations and I do not make any findings of fact," the judge said.

"Having considered all the relevant factors, I am satisfied that this is a proper case to issue the summons as requested," she wrote.

Referring to Mr Johnson as the "proposed defendant", Judge Coleman said he would be required to attend a preliminary hearing that could then result in a trial.

Mr Johnson is considered the favourite among the 11 candidates vying to replace the outgoing Mrs Theresa May as leader of the governing Conservative Party, and therefore prime minister, by the end of July.

The summons application made by Mr Ball's lawyers alleges that Mr Johnson "repeatedly lied and misled the British public as to the cost of EU membership" and "knew that such comments were false or misleading".

"Lying on a national and international platform undermines public confidence in politics."

The maximum penalty for misconduct in public office is life imprisonment.

Mr Johnson's lawyer said the pro-Brexit figurehead staunchly denied acting in an improper or dishonest manner.

Mr Johnson's position is that the application is a politically-motivated stunt as part of a campaign to undermine the referendum result, or to prevent its consequences, or both.

"The decision to summon Boris Johnson is extraordinary. It is not the role of criminal law to regulate political speech," said an unnamed source close to Mr Johnson, according to quotes cited by the Daily Mail newspaper's deputy political editor. "This runs counter to centuries of British political tradition and risks undermining our democracy."

Meanwhile, Mr Matt Hancock, one of the Conservative candidates vying for Mrs May's job, said he would renegotiate the future relationship with the EU and would explore the possibility of changing the Withdrawal Agreement.

The EU has said the Withdrawal Agreement negotiated with Mrs May, which she failed to pass three times in the United Kingdom's Parliament, is not up for negotiation, although the non-binding agreement about future relations after Brexit may be amended.

AGENCE FRANCE-PRESSE, REUTERS