Two private investigators have been arrested on suspicion of bribing a Scotland Yard anti-corruption officer.
The suspects, aged 53 and 58, both previously served with the force, the Metropolitan Police said.
They were held as officers from the force's directorate of professional standards raided the London offices of private investigation firm Risc Management Ltd, it is understood.
Mike Schwarz, a partner at Bindmans LLP, told the Home Affairs Select Committee of possible cash payments made by Risc Management Ltd to sources of theirs who were "presumably police officers or those close to the investigation".
The Metropolitan Police said later that a 45-year-old serving detective constable at Scotland Yard has also been arrested on suspicion of accepting payments from private detectives.