Commuters will continue to face delays until midday because of a broken down train at Berkhamsted between Milton Keynes Central and London Euston.
Signalling problems have also contributed to the travel chaos, which caused two-hour delays for city commuters this morning.
The latest update revealed trains to and from London Euston are being delayed by up to 30 minutes.
Southern trains are no longer affected by this disruption.
The routes affected include London Midland trains between Birmingham New Street/Milton Keynes Central and London Euston, Southern trains between Milton Keynes Central and South Croydon and Virgin Trains between Manchester Piccadilly / Birmingham New Street and London Euston.
Trains between Milton Keynes Central and Watford Junction are being delayed by up to 20 minutes. Virgin Trains will not be calling at Watford Junction.
London Midland passengers may use Chiltern Railways, CrossCountry, East Midlands Trains and Virgin Trains services on reasonable routes.
Virgin Trains passengers may use Arriva Trains Wales, Chiltern Railways, CrossCountry, East Coast, East Midlands, First Great Western, London Midland and Northern rail on any reasonable routes.