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.
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The Duke and Duchess of Cambridge treated their son Prince George to a festive day out in Norfolk over the weekend.
Remaining cloudy but mostly dry with strong winds and mild temperatures.
A couple from Essex had to be pulled out of mudflats by an RAF rescue helicopter after they got stuck while walking their dog.