The theft was discovered in the early hours of Monday, 13th April, by Network Rail engineers investigating multiple signal failures.
Detectives believe it was stolen several hours earlier, between 11pm and midnight on Sunday, 12th April.
Detective Constable Bob Hunt, investigating, said: “Late on Sunday, we believe a person or persons gained access to the railway line via Westfield Road, just north of Retford station. Eighty metres of live cable was stolen from the trackside.
“The theft caused major disruption on the East Coast Main Line on Monday morning as the cable connected vital track circuits and signalling equipment. It caused 2,822 minutes of delay, affecting 143 trains. Six train services were fully cancelled with a further six partially cancelled. The total cost of the disruption to the rail industry was £440,783.
“While rates of metal and cable theft from the railway have fallen significantly in recent years, we continue to work closely with the rail industry to bring offenders to justice and reduce disruption for passengers.”
Officers are keen to speak to anyone who saw anything suspicious around Retford station late on Sunday evening or early on Monday morning.
DC Hunt added: “I am keen to hear from local residents and anyone else who was in the vicinity of Retford station late on Sunday. Did you see anything suspicious? Were there any people or vehicles in the area that you have not seen before? If you have any information, however trivial it may seem, please get in touch with BTP.”
Anyone with information about this incident should contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference P/B6 of 17/04/2015. Alternatively, information can be passed to the independent charity Crimestoppers anonymously on 0800 555 111.
A spokesman for Network Rail said: “Cable theft causes massive disruption as passengers and freight services are interrupted and is hugely costly to the industry, as this case in Retford demonstrates. The financial cost has to be recovered from elsewhere, reducing the investment we are able to make to improve services.
“We are proud of the reduction in cable theft in recent years but we are not complacent, and we will continue to make every effort to protect the rail network from thieves by working closely with the BTP. The Scrap Metal Dealers Act, introduced in 2013, has also made it much harder for thieves to profit from the crimes they commit on our railways.”