U.K. Conservative Party leadership contender Boris Johnson must attend a court hearing to face allegations of misconduct in public office, a London judge ruled.

The judge said Wednesday that a private prosecution attempt can proceed against the politician. District Judge Margot Coleman said this is a "proper case to issue the summons." Johnson will be required to attend Westminster Magistrates Court for a preliminary hearing, she said.

"The allegations which have been made are unproven accusations and I do not make any findings of fact," the judge said.

The unprecedented attempt to privately prosecute Johnson could be an embarrassment for the politician, who is the favorite to succeed Theresa May when she formally resigns as leader of the Conservatives and U.K. prime minister.

Campaigner Marcus Ball is trying to bring charges against the member of Parliament after his "infamous" claim that the U.K. sent 350 million pounds (US$442 million) per week to the EU -- one of the central tenets of the Brexit campaign.