A teenage thug who held a knife to a youth's throat during a robbery and was involved in a vicious attack on a train driver has been locked up for 12 months.

Mitchell Longhurst, 17, also robbed a 15-year-old boy travelling alone on another train and spat in the face of a police officer.

But, despite the fact he was on bail for the offences at the time, and that the effect on his victims was likely to be considerable, a judge told Longhurst he had been "persuaded" to pass what might be viewed as an "unduly lenient" sentence.

Judge David Griffith-Jones QC, sitting at Maidstone Crown Court, said he was able to impose a 12-month detention and training order in light of the nine months Longhurst had already served on remand - as well as his significant progress while in custody at HMP Cookham Wood in Rochester.

Longhurst - of no fixed address, but formerly of Jefferson Road, Sheerness - admitted robbery, possession of an offensive weapon and common assault in Sevenoaks on December 7 last year, two offences of criminal damage on Sevenoaks-bound trains on January 9 and 22 this year, a public order offence involving the train driver attack, again on a Sevenoaks-bound train on January 22, and another robbery on January 21.

Passing sentence, the judge told Longhurst he had played a leading role in both robberies, committed when he was just 16.

"Anyone who uses a knife to threaten someone else runs the risk of matters escalating considerably and thereby causing serious injury," he said. "It is fortunate for you that things did not escalate."

"Anyone who uses a knife to threaten someone else runs the risk of matters escalating considerably and thereby causing serious injury. It is fortunate for you that things did not escalate..." - Judge David Griffith-Jones QC

Judge Griffith-Jones added it was also "unfortunate" that neither of the robbery victims had provided victim impact statements.

However, the court was told train driver Mark Kerins had been left feeling suicidal and might never be able to return to driving trains again.

He was attacked after remonstrating with a group of youths who were preventing his train from leaving by keeping the doors open.

"The incident has had a tragic effect," remarked Judge Griffith-Jones. "He describes his whole life being changed and how he had been happy-go-lucky and strong-willed.

"Since the incident he has been on medication to help him sleep and ease his anxiety, and is undergoing counselling.

"Not surprisingly, he describes how the effects have impacted on his relationship with his partner and children."

The court heard that following Longhurst's arrest, police found two knuckle dusters at his accommodation.

Despite one having partial DNA on it matching Mr Kerins, the judge said he was sentencing Longhurst on the basis he was not the person who attacked Mr Kerins.

Longhurst, who at one time was also living in bed and breakfast accommodation in Rochester High Street, has previous convictions for assaulting police, criminal damage and battery.

The judge told him he will serve up to half his sentence behind bars.

Also in the dock with him was Billy Wiltshire, 18, of Stofield Gardens, Mottingham, south east London.

"He is a very different young man, and a young man who seems to have grown up rather rapidly while on remand..." - Philip Sinclair, defending

He admitted one offence - robbery of the 15-year-old boy on January 21 - and was sentenced to a 24-month youth rehabilitation order, with conditions including a tagged four-month curfew between 10.30pm and 7am, and to attend a Thinking Skills programme.

Philip Sinclair, defending Longhurst, said the teenager had been "well-behaved and well-adjusted" until cannabis use and problems at home led to a spate of offending.

However, he added that custody had given Longhurst stability. "He is a very different young man, and a young man who seems to have grown up rather rapidly while on remand," said Mr Sinclair.

Jonathan Rosen, defending Wiltshire, said he was heavily in drink at the time of the robbery and could not explain why it was committed.

"But he accepts his presence and standing by his friend, and that by effectively offering support and encouragement he was party to the joint enterprise."

Mr Rosen added that Wiltshire, who works for an international removal firm, was "utterly wracked" with guilt and had resorted to self-harm.