Police were called to Hampstead High Street this afternoon after reports of a robbery at the post office.

A witness described how a man ran out of the post office carrying a bag and, as he escaped, he hit the security guard in the face who collapsed to the ground bleeding.

Mohammed Khan was posting a parcel at the time.

He said: “There was a scuffle and then I heard cries and shouts and saw a man running away. I tried to trip him up and then chased him down the road with the security guard. The guard collapsed after he was struck and I ran as fast as I could but I couldn’t keep up.”

He added: “I don’t know if he had a weapon. When you have a gut feeling you don’t think, you just do it.”

Police confirmed they were called to the scene of the incident at 1.42 this afternoon.