Commuters from King's Lynn were delayed on Wednesday morning when signalling problems affected trains to London's King's Cross.
Problems hit during the peak rush hour and trains were halted for around an hour while repairs were carried out in the Ely area by Network Rail.
A spokesman for First Capital Connect, which runs the service, said trains continued to run from Ely, although there were delays, but buses were provided from King's Lynn to Ely while the work took place. Trains were running again at 9.45am.
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