A man was arrested in Portsmouth as part of an operation in which a serving police officer and four others were held on suspicion of bribery.
The 49-year-old constable works in Scotland Yard’s Specialist Operations team, which covers counter-terrorism, airport security and guarding ministers and other public figures.
He is accused of abusing his position in the force in order to get other work.
Deputy Assistant Commissioner Fiona Taylor said: “The investigation has led us to believe that a serving police officer may have been abusing his role within the Met to position himself within the commercial sector.
“What advantage, if any, he obtained through the relationships he sought to cultivate will be established through our ongoing work.”
The officer was held on Tuesday on suspicion of misconduct in public office and bribery; and the four other men were held on suspicion of aiding and abetting misconduct in public office and bribery.
Three, aged 46, 53, and 73, were arrested at a London police station, while the fourth, aged 62, was held in Portsmouth.
Watchdog the Independent Police Complaints Commission has been kept informed of all developments in the inquiry, Scotland Yard said.
The force refused to release further information at this stage “to protect the investigation”.