Rail travellers on busy commuter routes suffered delays today because of a fresh incident of cable theft.
Services to and from London's Liverpool Street station were hit after overhead cables were targeted by thieves near Cheshunt in Hertfordshire.
Network Rail engineers were working to repair the damage.
The incident is the latest in a series of thefts which have caused huge disruption to rail services in many parts of the country over the past year.
British Transport Police and rail companies have launched campaigns to warn of the dangers of stealing cable from railway lines, but crimes continue to be committed.
There were also difficulties for travellers on the Underground's Metropolitan line during the morning rush-hour.
A signal problem at Baker Street led to a part-suspension of the line between Wembley Park and Aldgate for a time and there were long delays on other parts of the line.
There were also minor delays on the Tube's Victoria line due to a faulty train at Stockwell in south London.
British Transport Police said the incident was reported at 5.15am today by a passing train driver who noticed a fire by the side of the line.
Officers attended the scene, with London firefighters and engineers from Network Rail, and discovered around 1,200 metres of copper cable had been stolen.
A British Transport Police spokesman said: "There is a common assumption that cable theft is a victimless crime, with the only effects being felt by the railway industry. This is not the case.
"Theft of cable can, and does, cause significant delays and cancellations to the rail industry - as well as costing the industry millions of pounds each year.
"What thieves don't realise is that they're attempting to steal cable, sometimes live, carrying up to 25,000 volts. Not only are they risking a court appearance, they're also risking their lives."