Trains are delayed between Welwyn Garden City and Alexandra Palace this morning after a signalling fault.
Great Northern confirmed a "fault with the signalling system" was causing delays of up to 15 minutes between both stations.
Delays are expected to last until 10am.
"A fault with the signalling system between Alexandra Palace and Welwyn Garden City is causing disruption to journeys running through these stations," read an update from Great Northern.
"As a result, trains may be delayed by up to 15 minutes or revised. This is expected until 10am.
"Please leave 15 minutes extra to complete your journey if you are travelling this morning, due to the disruption some services may be cancelled or revised at short notice. You may need to use more than one train to complete your journey."
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