A daredevil lay down between railway lines between Hitchin and Letchworth as a train rolled over them on Halloween night, transport police believe.

The incident at about 9pm last night meant trains on the line were affected by long delays up to 11pm, with passengers on the 8.44pm service from London King’s Cross to Cambridge told by the driver that a “body or prank body was lying in between the tracks”.

British Transport Police said they were called at 9.17pm to reports that a train had struck a person at the Hitchin flyover, but that a search involving other emergency services and a police helicopter had found no trace of anybody.

A spokeswoman said: “There’s nothing to suggest that it was a fake body – the current investigation looks as though someone was trespassing on the line and the train went over them, without injuring them.

“We are now investigating and ask anyone with information to get in contact.”

The scene was clear by 10.49pm.

A passenger who was on the train involved told the Comet he had seen ambulances and paramedics go past his carriage while they remained at a standstill between Hitchin and Letchworth for about half an hour.

He said: “It was Halloween. It could be a matter of someone playing a stupid, stupid prank, or it could be someone who was trespassing in between the tracks.

“I think I could fit in between the lines, so I think that’s definitely plausible – but I don’t know much about how the railway works.

“If we did go over something, I’m sure we would have known. I’d have thought if it actually was someone there they would have stopped at Letchworth, called it a night and taken a report from the driver.”

The train continued to Letchworth and then on with the rest of its journey.

A Great Northern spokesman said: “On the face of it, this was a hugely irresponsible act which would have been very frightening for our driver.

“It delayed passengers on the train by an hour and a half, causing some to miss their last connections at Cambridge, and wasted precious ambulance, police and rail staff time and resources as we sought to ensure the safety of the person involved.”

Anyone with information about the incident should text British Transport Police on 61016 with reference 626 of October 31.