Police have announced that no charges of misconduct in public office will be brought against politicians who may have used inside information to bet on the general election debate.

However, a statement from the Metropolitan Police said the Gambling Commission would continue to investigate potential breaches of the Gambling Act, which is overseen by the betting watchdog.

The investigation began after The Guardian revealed that Craig Williams, Rishi Sunak’s parliamentary private secretary and a Conservative MP before he lost his seat in July, had placed a £100 bet on a July election three days before the prime minister announced the date.

Williams and another candidate, Laura Saunders, eventually lost formal party support after it emerged they were being investigated by the Gambling Commission.

Also being investigated are bets allegedly made by Tony Lee, the Conservative campaign manager who is married to Saunders, Nick Mason, the Tories’ chief data officer, and Russell George, a Tory member of the Welsh parliament who represents the same area as Williams.

Seven Met police officers were also investigated over allegations they used inside information to place bets on the election date.

In addition to the Gambling Commission investigations, the Met considered whether other offences, particularly misconduct in public office, might apply. A “small number of matters” thought to be potentially relevant were assessed by detectives before seeking advice from the Crown Prosecution Service, the Met statement said.

“Based on the assessment of the evidence and the advice of the CPS, it was determined that the high threshold for misconduct in public office to be proven was not met,” it added.

“It has therefore been agreed between the Met and the Gambling Commission that the most appropriate offences to proceed with are those falling under the Gambling Act. The Met’s involvement in investigating any criminal matters will now come to an end and the matters will be referred back to the Gambling Commission for further investigation.”

Detective Chief Inspector Katherine Goodwin said: “These allegations have caused a significant dent in public confidence during the election campaign and it was right that they were investigated to identify any possible wrongdoing.

“While our involvement in the criminal investigation now comes to an end, it is important that this is not misinterpreted as an ‘all clear’ for those whose cases have been reviewed. There are still breaches of the Gambling Act that need to be considered and it is appropriate that these are dealt with by investigators from the Gambling Commission who have specific expertise in this area.

“Seven police officers accused of placing bets remain among those under investigation by the Gambling Commission. They also remain under investigation by the Met’s Directorate of Professional Standards.”

A section of the Gambling Act that deals with cheating can involve someone attempting to improve their chances of winning a bet by using insider information. If found guilty, someone could face up to two years in prison.