A big rise in the theft of copper cable from railways is causing delays and costing rail companies £3m, British Transport Police (BTP) say.
Thieves have been stealing cable from warehouses or from along tracks
There were almost 1,000 incidents of theft of signalling cable from warehouses or from along rail lines this year - a 50% rise on 2005.
BTP Assistant Chief Constable Paul Robb said the thieves were "putting their own lives at risk".
The crime is most common in the north-east of England, police say.
BBC business correspondent John Moylan said there was no threat to the public as a result of the thefts.
"People are ripping out the high voltage cabling which controls things like the communications system, the points and the signalling system.
"I'm told there's no threat to the public in all of this in as much as there are fail safe systems.
"Each time an incident happens it can cause delays for something like 10,000 passengers."
The BBC understands there have been two fatalities associated with copper theft from railway sub-stations and several people have been severely injured.
"The railway is not an environment where people should go," ACC Robb said.
"Some of the people have gone at night time, assuming that there aren't any trains - well of course there are, there are engineering trains."
He added there was a "great concern" people were risking their lives to steal copper and warned that the risk was not worth it.
Copper thieves are not only targeting the rail network but also homes.
One victim, Charles Bull, woke to the smell of gas and found that thieves had stolen the pipes supplying his home.
He said: "I got up at a quarter past six in the morning and I realised that we'd got no gas in the house.
"I thought the boiler had gone off and after trying to re-light it I came out here and there was the sound of gas hissing out of the pipe.
"I looked down the side here and realised the gas pipe had been taken off the side of the house."