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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Dry and sunny, with very light winds and temperatures quickly rising after a rather cool start in some rural locations.
Settled weather continuing. Warm on Sunday.
Four people arrested in connection with the death of a man in Chelmsford have been released from custody.