A judge who locked up a 16-year-old boy for four years issued a strong warning to robbers targeting youngsters with mobile phones.

Bradford Crown Court heard how Lee Farrell demanded money, phones and trainers from younger boys who were frightened into handing over their possessions by threats that he had a knife or CS gas on him.

The court heard that Farrell, of Landford House, Little Horton, was a persistent offender.

Judge Roger Scott highlighted the fact that such offences were on the increase in Bradford and he told Farrell: "It is time that people like you, young though you may be, learned that if you do this you are going to get locked up for a very long time.''

Judge Scott said over the last 15 months he had had a number of young men in court involved in robbing 13- and 14-year-old boys of their phones and possessions.

Farrell even committed further offences of attempted robbery and robbery after he was arrested and questioned by police about a robbery involving two 14-year-old boys on Septem-ber 16 last year.

The court heard how those boys handed over about £10 and a phone after Farrell and a female approached them near the city's ice rink.

During that robbery the girl with Farrell told the boys that he had a knife on him.

Prosecutor Robert Blantern said Farrell was released after questioning but a few days later he approached another 14-year-old boy in Forster Square and demanded money and his trainers but he refused.

Mr Blantern said minutes later Farrell confronted a 13-year-old boy in Bank Street and when he again threatened to use CS gas the boy handed him £40.

Farrell pleaded guilty to three offences of robbery and one of attempted robbery.

Since last November he has been detained at a secure unit near Durham.

His lawyer Lesley Dickinson said he was remorseful.