An earlier fault on a train at Watford Junction has now been rectified.
As service recovers, trains running between Milton Keynes Central and London Euston may still be delayed by up to 20 minutes.
Disruption is expected until 18:45.
Check before you travel:
You can check your journey using the National Rail Enquiries real-time Journey Planner
Compensation:
You may be entitled to compensation if you experience a delay in completing your journey today. Please keep your train ticket and make a note of your journey, as both will be required to support any claim.