Services between Stevenage and London are being affected by a safety inspection at Knebworth Picture: Nick Gill (Image: Archant)
There is currently disruption for trains between Stevenage and London as a safety inspection is carried out in Knebworth.
A problem with the track was reported earlier this morning, and Network Rail engineers are now on site to assess and repair the problem.
This mean most trains will need to use the slow line, which is causing congestion.
It affects Thameslink and Great Northern services, as well as some longer-distance operators.
Disruption is expected until 8.30am.
You can still use your normal route for travel, and all stations are being served - although trains may depart in a different order or leave from a different platform at your station.
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