Passengers on a London to Scotland railway line endured further delays and cancellations today.
The latest incident on the West Coast Main Line involved a signalling problem in the morning rush-hour between Leighton Buzzard in Bedfordshire and Cheddington in Buckinghamshire.
This affected services run by London Midland and Virgin Trains who have been hit by continuous service disruptions in recent days on a line on which Network Rail (NR) has just completed a £9 billion upgrade.
A Virgin spokesman said today: "We have had to cancel three trains out of Euston station (in London) and two trains - one from Birmingham and one from Manchester - could go no further than Milton Keynes (in Buckinghamshire).
"We would like the West Coast to settle down so that we can provide our customers with the good service to which they are entitled. We share their frustration."
An NR spokesman said: "There was a minor problem with points this morning near Leighton Buzzard. As part of the project to upgrade the West Coast Line, additional flexibility has been built into the system which is allowing NR Rail to continue to run trains.
"Typically, in this situation a small number of services will be cancelled to allow the bulk of the timetable to run as normal and keep delays to a minimum.
"As part of the standard rapid response service, engineers were at the site and fixing the problem in less than 30 minutes. Services are returning back to normal. We apologise for any delay caused to passengers."
Meanwhile, NR engineers continued to investigate the series of problems that have plagued the line.
NR said the failures were each caused by different faults, discounting suggestions that they stemmed from any rush to complete the £9 billion upgrade by the end of the year.
Passengers were hit yesterday when an overheard wire problem in Atherstone, Warwickshire, caused long delays for passengers on Virgin Trains and London Midland.
The line between Milton Keynes, Buckinghamshire and Rugby in the West Midlands was also shut for part of the morning after a lorry hit a railway bridge at Blisworth in Northamptonshire.
Trains were diverted via Northampton, causing minor delays.
NR staff had just finished dealing with an overhead power problem near Wembley in north west London which prevented Virgin and London Midland running any trains in or out of London's Euston station for the first part of Wednesday.
Before the Wembley incident, the West Coast line suffered overhead cable problems at Bletchley in Buckinghamshire and at Rugby, which hit services on Tuesday.
Before that, West Coast services on Sunday and Monday were affected by overhead cable problems at Watford in Hertfordshire and the line was shut for a period after a light plane crashed close to the tracks near Stafford on Friday in an accident which claimed three lives.
The West Coast problem was just one of a series of disruptions to main line rail services today.
Trains run by the Southern rail company and by Gatwick Express were affected by an electrical supply problem in the Balham area of south east London which disrupted services between Streatham and Victoria station in London.
Southern passengers also had to contend with problems caused by a broken down train near Ashtead in Surrey. This also affected South West Trains' (SWT) passengers.
Southern passengers had to travel by bus between Horsham, Dorking and Epsom, and buses also had to be laid on for SWT customers for journeys between Effingham Junction and Leatherhead.
Southeastern passengers endured delays between Hastings and Tunbridge Wells after a signalling problem in the Etchingham area of East Sussex. Services into London's Charing Cross and Cannon Street stations were affected.