A total of 35 cases of credit card misuse are being investigated
More than 300 Metropolitan Police (Met) detectives have been investigated on suspicion of misusing corporate credit cards, following an audit of the force.
Of these, 46 cases have become criminal investigations overseen by the police watchdog the Independent Police Complaints Commission (IPCC).
The audit had been commissioned by the Metropolitan Police Authority which discussed its findings on Monday.
A spokesman said the force had no comment to make.
The Metropolitan Police gave 3,533 American Express credit cards to its officers and staff in 2003, in an attempt to reduce bureaucracy as they claimed expenses necessary for their jobs.
The Met withdrew 1,400 credit cards after finding almost £2m of police expenses unaccounted for.
The credit cards were then issued in 2006 to detectives from specialist operations, which includes counter-terrorism and those involved in diplomatic and royalty protection.
The scheme was extended to the specialist crime directorate, which investigates organised crime.
A report by the head of internal audit at the Metropolitan Police Authority, said: "In excess of 300 police officers have been referred to the Directorate of Professional Standards [DPS] by my staff and 46 of these have become formal investigations overseen by the Independent Police Complaints Commission."
Last year, former detective sergeant John Gallagher, 52, was sentenced to an eight-month prison term suspended for two years for misconduct in public office after spending £9,622 on his card.
Former detective sergeant Richard De Cadenet, 49, was jailed for 10 months after pleading guilty to misfeasance in public office. He spent more than £70,000 on his card.
One officer is awaiting trial and eight officers have received written warnings.
Jenny Jones, Green Party member of the Metropolitan Police Authority (MPA), said: "Well done to the current auditing team for uncovering this, but what on earth was happening before? Why was there no accountability?
"It beggars belief that our police, who are supposed to be solving crime, are suspected of fraud on a grand scale."