The Metropolitan Police is on high alert following a significant security breach that led to officers' and staffs' details being hacked.
All 47,000 personnel have been notified about the potential exposure of their photographs, names, and ranks, The Sun newspaper reported.
The breach occurred when cybercriminals managed to infiltrate the IT systems of a contractor responsible for printing warrant cards and staff passes.
In response to the report, a spokesperson for the Metropolitan Police told Sky News: "We have been made aware of unauthorised access to the IT system of a Met supplier.
"We are working with the company to understand if there has been any security breach relating to Metropolitan Police data."
Rick Prior, vice chair of the Metropolitan Police Federation, said any potential leak "will cause colleagues incredible concern and anger".
"We share that sense of fury... this is a staggering security breach that should never have happened," he said.
"Given the roles we ask our colleagues to undertake, significant safeguards and checks and balances should have been in place to protect this valuable personal information which, if in the wrong hands, could do incalculable damage.
"The men and women I represent are justifiably disgusted by this breach. We will be working with the force to mitigate the dangers and risks that this disclosure could have on our colleagues. And will be holding the Metropolitan Police to account for what has happened."
The company had access to names, ranks, photos, vetting levels and pay numbers for officers and staff, the Met said.
It added that the company "did not hold personal information such as addresses, phone numbers or financial details".
"Security measures have been taken by the MPS as a result of this report. The MPS has reported the matter to the National Crime Agency. The Information Commissioner's Office is also aware," the Met said.
The Sun also reported that the National Crime Agency had been called in amid fears terrorists or organised gangs could use the stolen data.
Met Police Service bosses also sent a message to their staff, urging them to "remain vigilant".
It remains unclear whether the hackers demanded a ransom from the printing company or were attempting to target officers and staff.
The incident comes after a redacted version of a leaked document that listed the names of police officers in Northern Ireland was posted on a wall facing a Sinn Fein office in Belfast in a "sinister" attempt to intimidate one of its politicians.
The document, which had mistakenly been shared online, included the names of around 10,000 officers and staff.