Footage of the incident was circulated on social media and police are urging anyone with information to come forward.
An investigation is ongoing and so far there have been no arrests.
People can report information by calling 101 with the reference CAD 6640/12 Oct or calling Crimestoppers anonymously on 0800 555 111.
Issuing guidance on checking the identity of a police officer, the Met said: “Unfortunately, there have been occasions when fraudsters have posed as police officers, both in person and on the phone, to trick people into giving them personal information and defraud them of money.
“If one of our officers contacts you in person, they’ll show you their police warrant card. This is proof of their identity and authority.
“Remember if you’re unsure about whether the person you’re dealing with is a genuine police officer – stop – and call us on 101 to check their identity.”
In an emergency people are advised to always call 999.