The helicopter will cover overground sections of the Tube

Police say Operation Rhino has reduced trespassing on the District Line's eastern stretch over the last three years and the scheme is being extended.

The helicopter will cover all of London Underground (LU)'s overground lines, depots and sidings over Easter break.

Lessons on Tube safety will also be on offer at stations in north-west London.

In December the Rhino helicopter used its heat-seeking equipment to trace two people who had broken into a depot.

'Not a prank'

Its cameras then directed police officers on the ground to their hiding place and they were arrested.

Operation Rhino is a partnership between British Transport Police (BTP), LU and Scotland Yard's Air Support Unit.

Police say the school holidays and lighter evenings tempt more youngsters out onto the tracks.

Chief Inspector David Dickason, of BTP, said throwing "missiles" at trains was not a prank.

"Trespass on the railway is a serious business," he said.

"It endangers not only the underground passengers and staff but the trespassers themselves."