A reported "trespasser on the track" stopped trains through Potters Bar this morning (June 4), with all lines through the station being blocked.
Emergency services, including teams from Hertfordshire Police and the British Transport Police, are attended the scene at the time of the incident.
Helicopter and canine teams had been utilised, to help police find the intruder.
Eventually, trains began to move through the area, but only at reduced speeds.
Rail replacement buses were also arranged whilst the incident was being dealt with.
A spokesperson for Great Northern Rail said at the time: "Trains are now moving through the area again, running at reduced speeds.
"We're working hard to get the backlog of queued trains on their way as soon as possible, however this will take some time.
"All lines have now reopened, and we're working to return to our scheduled timetables.
"Please continue to check journey planners before you travel, as your train may still be affected."
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