Maintenance workers 'could be killed or injured'
Railway Safety chief executive Rod Muttram said four workers had been killed in recent months and there could be further deaths and injuries unless action is taken.
He said government and commercial pressure to expand the railway system and get it running smoothly means too much work is being done too quickly.
The safety boss's warning will put pressure on the government to revise its timetable for improvements or consider reducing train services to cut the risk to workers.
Deadly game
Mr Muttram said crews are being forced to work near live rails because of pressure to keep trains running around the clock.
He said that in some areas 125mph trains can only be spotted 12 seconds before they reach workers, forcing them to play a potentially deadly game of roulette.
The safety boss said workers must be given more time to carry out their work, without the threat of live rails or fast moving trains.
The message will not be a popular one at a time when the government has called for a 50% increase in passengers over the next 10 years and an 80% increase in freight.
'Safety risks'
Mr Muttram's warning also came at a time when train company chiefs and passenger groups are already concerned about "real safety risks" following the collapse of Railtrack.
Stewart Francis, chairman of the Rail Passengers Council said: "It could be 12 to 18 months before we see a new network operator emerge.
"In the meantime, the best we can hope for is that the network does not deteriorate any further."