The shuddering impact when the train ran into the 9st concrete block and 10ft metal bar that Thomas Kerr and Joe Lynch had laid on the lines sparked terror in the carriages – and could have led to a major disaster.

At Peterborough Crown Court yesterday, Judge Sean Enright overturned the ban on naming Kerr (17), allowing The Evening Telegraph to reveal his name for the first time.

At the end of the trial last month, he had lifted the identify bar on his accomplice Lynch (16).

Judge Enright also hit out at the maximum penalty for the offence, saying two years was not enough.

He said: "Complicated sentencing guidelines for youngsters have become an obstruction to justice."

A jury had already found Lynch, of Blackmead, Orton Malborne, Peterborough, guilty of endangering the safety of rail users by putting the obstacles over railway lines at Black Bridge, in Stanground, Peterborough.

Kerr, of Kings Road, Fletton, Peterborough, had pleaded guilty to the same charge.

However, the pair were both cleared of the graver offence of endangering the safety of railway users with intent, which they had denied.

The court had earlier been told how one of the teenagers snapped a photo of their handiwork on a mobile phone, moments after the train struck the items on October 22 last year.

Judge Enright said Kerr was the "prime mover", while Lynch was an "eager and willing participant".

Sentencing them to 12-month detention and training orders each, he said: "You were part of a small group who used to hang around Black Bridge, and started to stray onto the railway line and put items on the line, watching as the train passed over.

"You both went up on to the track and both laid a concrete slab and metal bar on the track.

"A photo was taken by one of you of the slab and metal bar in position, with the train a small speck in the distance."

He added: "What was done was carefully thought through."

The terrified train driver spotted the obstructions and slammed on his brakes, preparing for derailment.

Judge Enright said: "By good chance no one was injured, but the passengers were shocked, frightened and hugely inconvenienced."

Defending Kerr, Georgina Gibbs said he had accepted his part in the plot and was "very remorseful".

Simon Gladwell, for Lynch (16) said he had been "naive" but didn't participate in placing the items on the track.

Speaking after the case, Detective Constable Paul Menarry said: "There is no doubt these two young men will not go down that route again.

"The judge did say in court he didn't believe that the maximum sentence should be just two years, but he applied the law as he could.

"I believe this will be a deterrent to others."

And he issued a strongly worded warning to would-be vandals.

"Don't go on to railway tracks and don't place items on the track, small or large, because it could have a disastrous effect," he said.

"If you do, you will be caught and you will go to prison.