The charges relate to an altercation near the signal box on December 28, when a signalman saw a dispute between a group of teenagers and intervened to help a 15-year-old he believed was being threatened.

DC Neil Barnes, investigating officer from the British Transport Police, said: "The teenager took refuge in the man's signal box before the gang forced their way in.

"As the signaller tried to push the youths out of the signal box, the struggle resulted in vital signalling equipment being damaged.

"The damaged equipment left staff sightless to oncoming traffic in the area.

"Had it not been for the prompt actions of the signaller in reporting the incident and initiating the emergency procedure to allow another nearby signaller to take over, we may have seen far worse consequences."

Ashley Fensom (19), of 14 North Everard Street, Lynn, admitted endangering safety on the railways and was sentenced to three months imprisonment, suspended for 12 months, during a hearing at Lynn Youth Court on Tuesday.

He was also given a community order and ordered to pay £150 in costs.

A 16-year-old from Downham admitted endangering safety on the railway and criminal damage and was given an eight-month detention and training order.

A 17-year-old, also from Downham, admitted endangering safety on the railway and was given a 12-month community order with 80 hours unpaid work. He will also pay £150 costs.

DC Barnes added: "We have worked very closely with Norfolk Police to identify the offenders and with the Crown Prosecution Service, who offered robust support in prosecuting the individuals for an extremely serious offence."

A spokesman for Network Rail said: "Any form of antisocial behaviour which injures, intimidates or endangers the lives of rail staff or passengers is not tolerated by Network Rail. "The sentence handed down reflects the serious nature of the offence committed."