Trains travelling on the Great Northern line are expected to be delayed for the next three hours due to signalling problems at Hitchin.
Operator Govia Thameslink Railway has said there are currently delays of up to 30 minutes on trains travelling between Stevenage and Peterborough or Cambridge.
Lines have now reopened but the company has said there could be delays through to 12 noon, as well as tweeting that delays are expected until 1.30pm.
Follow @GNRailUK for the latest updates.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here