London's Metropolitan Police are investigating "a small number of bets" made on the timing of the national election, with at least seven of its own police officers identified as having placed such wagers.
"We have agreed a joint approach with the Gambling Commission, who are the appropriate authority to investigate the majority of these allegations," Detective Superintendent Katherine Goodwin said in a statement on Thursday.
"There will, however, be a small number of cases where a broader criminal investigation by the police is required."
As well as breaching gambling regulations, these cases could involve additional offences such as Misconduct in a Public Office, the Met said.
The Met said it had compared the names of those who placed bets on the timing of the election against a list of their officers and so far, seven had been identified.
One, a member of the special protection unit who media have reported was one of Prime Minister Rishi Sunak's bodyguards, has been arrested.
Earlier this week, both Sunak's Conservatives and the opposition Labour Party withdrew support for candidates who are being investigated over bets relating to the July 4 election.
Two senior Conservative Party officials are also being investigated.
"We are focused on an investigation into confidential information being used to gain an unfair advantage when betting on the date of the general election," Gambling Commission chief executive Andrew Rhodes said.
"Our enforcement team has made rapid progress so far and will continue to work closely with the Metropolitan Police to draw this case to a just conclusion."