Network Rail have confirmed that 1,000m of cable has been stolen from the line between Bedford and Bletchley.
A spokesman told ITV Anglia that rail delays would continue for the rest of the day while engineers worked to make repairs.
More top news
Ipswich Town legend Kieron Dyer sits down with ITV News Anglia's Donovan Blake to look back at his extraordinary career.
The death of man in Witham in Essex is being treated as unexplained after a body was found in a river.
Turning cold and frosty overnight. Staying dry for much of the weekend but a snow warning comes into force on Monday.