Services may still be cancelled or delayed by up to 30 minutes, photo by Google Maps
A metal object struck the front of a train and damaged it - causing massive delays for commuters.
The incident occurred on the railway heading into St Albans.
Lines have now reopened following the removal of the object but delays of up to 30 minutes and a disrupted timetable are expected to remain until 6:30pm.
A Thameslink spokesman said: "We advise passengers to check journey planners before they travel and to continue to listen to onboard and station announcements.
"Any passenger whose journey is delayed by 15 minutes or more should claim Delay Repay compensation via our web site."
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