A points failure at Welwyn Garden City is causing disruption to trains northbound between Potters Bar and Stevenage this morning.

Train operator Govia Thameslink Railway was advised of the problem by Network Rail at 7.08am, saying some lines were blocked – with Great Northern services unable to run northbound between Welwyn Garden City and Stevenage.

But @GNRailUK has since tweeted to say all Network Rail has fixed the problem and all northbound lines have now reopened.

Train services may still be subject to delay or cancellation as the service recovers, with the operator expecting delays to continue until approximately 9.30am.

On the Great Northern website it says passengers with a Great Northern ticket can use it on the following services:

• Thameslink

• London Underground via any reasonable route

• Uno buses on routes 601 (between Welwyn Garden City and Radlett), 602 (between Welwyn Garden City, Hatfield and St Albans) and 635 (between Hatfield and Hitchin)

• London buses between London and Crews Hill & Elstree & Borehamwood

UPDATE 9.35am: Disruption is expected to continue until approximately 11am. London North Eastern Railway services are no longer affected by this incident.