Police have released CCTV of a security guard fighting back against a hooded man who attacked him from behind and robbed him of cash.
The 50-year-old can be seen clambering over chairs and using his helmet to lash out at the suspect who punched him in the face and stole the cash delivery.
He only managed to hit him in the arm before the man made his escape from Hampstead High Street post office in north London.
The video earlier shows the robber, a white man, enter and wait near the counter, dressed in a coat with the hood up and half his face covered.
The security guard was treated in hospital for injuries to his head and shoulders.
The Metropolitan Police Flying Squad has appealed for anyone who witnessed the 16 February robbery to call 020 8785 8655.