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 cancer patient who had a potentially life-saving operation postponed says he felt like doctors were "signing his death warrant."
Ipswich Town loanee Chris Wood says that the club are still confident of gaining automatic promotion to the Premier League.
A fine day with lovely spells of sunshine. Chilly with frost in places tonight.