Fifteen people including former Conservative MP Craig Williams have been charged with betting offences by the Gambling Commission.
The investigation was launched last year following bets placed on the timing of the 2024 general election.
The commission said the investigation focused on individuals "suspected of using confidential information - specifically advance knowledge of the proposed election date - to gain an unfair advantage in betting markets".
Before the election was called, Williams was the MP for Montgomeryshire and an aide to then-Prime Minister Rishi Sunak.