UK police on Thursday said officers will investigate a "small number" of bets made on the timing of the general election, as part of a joint probe with the gambling watchdog.

The announcement by London's Metropolitan Police heightens the possibility that politicians or party officials could be criminally investigated alongside police officers for placing bets on the election date.

The Met had already announced that one of its officers had been arrested on suspicion of misconduct in a public office and placed on restricted duties over election betting claims.

Six other officers have now been identified as having placed bets on the timing of the poll and are being probed by industry regulator the Gambling Commission.

In an update on the growing scandal on Thursday, the Met said its directorate of professional standards was being kept informed on those probes, while officers were also beginning to investigate cases.

"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.

"There will, however, be a small number of cases where a broader criminal investigation by the police is required," she added.

A furore around the issue has overshadowed the closing stretch of campaigning, as Prime Minister Rishi Sunak struggles to close his Conservative party's large poll deficit to the Labour opposition before the July 4 vote.

Sunak has said he is "incredibly angry" about the accusations at least two Tory candidates placed bets on the timing of the ballot based on private information, and has withdrawn support for them.

Political bets are allowed in the UK but using insider knowledge to make them is against the law.

Meanwhile Labour has also cut support for a candidate after it emerged he was being probed by the Gambling Commission over betting on the outcome of the contest in his own seat.

Summarising the approach to the joint investigation, the Met said the majority of cases are suspected breaches of gambling legislation and will be investigated by the commission.

But the force added its specialist crime unit will also probe a "smaller" number of bets "with specific features that could mean additional offences apply, for example misconduct in public office".