A fare dodger on the 149 bus punched a ticket inspector in the head and shouted: “The next time I see you, you will be a dead man.”

Horrified passengers were left to pull the man away and push him off the bus.

It happened in Stoke Newington at 1.20pm on January 5 after the inspector challenged the man about not having paid. The attacker refused to give his details, kicking his victim in the legs before punching him in the head and chest.

The bus was going down Rectory Road towards Manse Road at the time.

Two months on, Scotland Yard has released a picture of a man detectives believe has information about the attack.

The man they want to trace is described as black, about 40, 5ft 10ins tall, stocky and sporting a black moustache. He spoke with a “London accent”, police said.

He was pictured on bus CCTV in a brown cap.

Pc Neil Webb said: “If you commit such an offence, not only will you be prosecuted, but you may also be banned from being able to use TfL operated services in the future.”

TfL’s enforcement and “on-street operations” chief Graham Daley added his organisation was “extremely concerned by these allegations”.

Anyone with information is asked to contact Pc Webb on 07500 607652 or call Crimestoppers, anonymously, on 0800 555 111.