LONDON — One of Prime Minister Rishi Sunak’s police bodyguards has been arrested over alleged bets on the date of Britain’s national election made before it was announced, authorities said Wednesday.

The Metropolitan Police force said that a constable in the Royalty and Specialist Protection Command was arrested Monday on suspicion of misconduct in public office.

The arrest came after the Gambling Commission contacted the force. The commission, which regulates the gambling industry, confirmed it was investigating “the possibility of offences concerning the date of the election.”

Sunak announced May 22 that an election for Parliament would be held on July 4. The date had been a closely guarded secret and the announcement took many people in Sunak’s governing Conservative Party by surprise. Most had assumed the election would be held in the fall.

Betting is a popular activity in the U.K., with bookmakers offering odds on everything from sports to elections and the winners of literary prizes. Cheating by acting on inside information is a criminal offense.

The arrested officer was released on bail pending further inquiries and has been removed from duty while the force conducts its own investigation. The officer was not named. British police usually do not identify suspects until they are charged.

Last week Sunak aide Craig Williams, who is running to be reelected to Parliament, acknowledged he was being investigated by the Gambling Commission for placing a 100 pound ($128) bet on a July election before the date had been announced.

Williams said the regulator was making “some routine inquiries and I confirm I will fully cooperate with these.”

“I don’t want to be a distraction from the campaign, I should have thought through how it looked,” he said.