Damage to overhead wires at Welwyn North Station is causing disruption for commuters this morning.
The problem arose overnight, when workers were carrying out maintenance to the line.
Trains between Stevenage and London Kings Cross are being delayed by up to an hour, changed, or completely cancelled - the incident is not expected to resolve until midday.
Alternatively, there are services running between Welwyn Garden City Station and Hertford North or London, but they will not be stopping at Welwyn North or Knebworth.
However, there is a rail replacement bus operating between Stevenage and Welwyn Garden City which will be stopping at those stations.
A spokesperson from station manager Great Northern Railway apologised for the inconvenience, urged passengers to check train timetables before they travel and reminded affected commuters about the delay repay scheme.
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