Relatives of a man killed when he leant out of a train window as it entered a tunnel at 70mph, were today due to formally identify his body.

Passengers on the London Victoria to Worthing service witnessed the horrific accident at 12.15am on Saturday.

The 32-year-old man was seen to lean out of the train shortly after it left Hassocks station. He struck his head on the tunnel entrance.

The driver of the train reversed back to Hassocks, where ambulance paramedics tried in vain to save the man's life. He died of massive head injuries.

A spokesman for the British Transport Police at Brighton said: "A number of people on the train witnessed the incident and pulled the emergency cord. It is thought the man hit his head on the entrance to Clayton tunnel between Hassocks and Preston Park.

"The train was reversed back to Hassocks because that was the quickest way for ambulance personnel to gain access to the man.

"Despite their efforts, the man died. The death is not being treated as suspicious. The Health and Safety Executive and the local coroner have been informed."

There were a number of passengers on board and British Transport Police are urging witnesses to contact them 01273 328545 or 0207 3915275.

The tragedy is expected to reignite concerns about the safety of slam-door trains where the windows can be fully lowered.

They are due to be replaced by the end of 2004.