Armed robbers attacked a guard with a hammer as they raided a security van, making off with a cash box.
Two men are believed by police to have assaulted the guard outside Barclays bank in Chiswick High Road on Christmas Eve (December 24) at about 11.45am.
They took a cash box, the value of which is not known, from the G4S van before making off on a moped.
The victim is not understood to have been seriously injured in the robbery.
A police spokesman said the Flying Squad was investigating the raid but no arrests had been made.
Anyone with information is asked to call Crimestoppers, free and anonymously, on 0800 555 111.