Due to overnight engineering work not being completed on time, cancellations or delays are expected on the lines between Hitchin and Royston.
Great Northern and Thameslink rail announced that although most services are running as normal, some services have already experienced large delays and they predict some further delays of up to 20 minutes.
This will affect passengers at Hitchin, Letchworth Garden City, Baldock, Ashwell and Morden, and Royston.
The late-running engineering work, which was due to be ready between Royston and Baldock, is now complete.
However as carriages and crew aren’t in the right places due to the disruption, it will take time for the timetable to return to normal.
The disruption is expected to continue until around 9am.
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