From GNER:

"Train services between Doncaster and York are significantly disrupted due to a structural problem with a bridge.

"Trains between Doncaster and York will operate at approximately hourly intervals and journey times will be extended.

"It is not possible to operate the full GNER service and those trains that are running over their full route will be busier than normal.

"Network Rail's engineers are working to repair the bridge as soon as possible. However, the current estimate for a return to the normal service is 06:00 hrs Friday 28th September."

And as usual, FCC have more information that GNER haven't mentioned:

"On the Thameslink route there are delays due to earlier over running engineering work at London Bridge. In addition, a tree has fallen on the overhead power lines near St Albans. As a result two out of four lines are currently closed.

"Services are currently delayed by up to 30 minutes."

My colleague reports his Picadilly Line train not stopping at KX this morning due to 'overcrowding' (around 8.45).