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
Prince William starts his final shift as an air ambulance pilot before taking up his royal duties
Nurses have gathered in Cambridge to campaign to scrap the 1% pay cap imposed on them. The RCN says it's causing nurses to leave.
There will be some early morning sunshine before cloud starts to spill in from the west. Through the late morning showers will then develop.