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
A police dog who sustained serious injuries when he was stabbed by a fleeing suspect is retiring - a day after winning three trophies
An investigation has begun into what caused a helicopter to crash in the Welsh mountains
A dry day for most with sunny spells and it looks like it could be the warmest day of the year so far.