The victim, described by police as a family man from northwest London, was on his way to work when he was attacked. He was pronounced dead at the scene at about 4.30am.

Another man, believed to be a taxi driver, was critically ill in intensive care after attempting to intevene.

The attacker, a powerfully built 30-year-old Tunisian man, also lashed out at paramedics and police officers who tried to restrain him.

The assailant, who was not carrying a weapon, is thought earlier to have kicked down the door of a nearby café, made himself a cup of tea and watched cartoons on television before killing his victim farther down the road. He was eventually arrested and taken to a West London police station.

Other members of the public — two women and a man — were assaulted but suffered less serious injuries.

Two female paramedics were also injured, as were several police officers.

Gary Webb, a motorcyclist, arrived at the scene shortly after the attack. Mr Webb, one of several witnesses to the incident, said the suspect was standing over the dead man’s body.

He said: “I saw a man lying in the road. He was clearly dead so I went to help.

“There was an African man stood over him who was over 6ft tall, who was dressed in a suit and had a mad look in his eyes. His eyes were wild and he was really staring. It was frightening and I felt in danger.

“The man started to approach me and put his hand up towards his breast pocket. I felt intimidated so I got back on my bike and sped away.”

Mr Webb is believed to have happened upon the crime scene, in Harlington, 100 yards behind the large hotels that border the northern perimeter of the airport, shortly after the killing.

A spokesman for the London Ambulance Service said: “Shortly after arriving at the scene, our crew requested urgent police assistance. A further four ambulances, two rapidresponse cars and a duty station officer attended, and both crew members were taken to hospital, although thankfully neither was seriously hurt.

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