London Northwestern trains between Watford Junction and Milton Keynes Central have been impacted by a fault with the signaling system.
The railway operator has said that this has caused trains to run at a reduced speed.
A spokesperson for London Northwestern said: "Train services running through these stations may be delayed by up to 15 minutes."
Disruption is expected to last until around 12:00 today (6/9).
📢 Problems reported— London Northwestern Railway (@LNRailway) September 6, 2021
🚧 Delays to services between Watford Junction and Milton Keynes Central: Due to a fault with the signalling system between Watford Junction and Milton Keynes Central trains have to run at reduced speed.