An entire fleet of commuter trains was withdrawn from service today, causing travel chaos for thousands of passengers.
Silverlink County Trains withdrew its fleet of Class 321 trains due to safety concerns "loose bolts" in the braking gear and suspended all its services between Birmingham and London Euston.
A statement on the service's website reads: "Following precautionary examination overnight on Silverlink County Class 321 trains, a decision has been taken on safety grounds to immediately withdraw the entire fleet for further examination to part of the train braking gear.
"As a consequence of this Silverlink County is unable to operate any train service today between Birmingham, Northampton, Milton Keynes, Watford and London Euston."
Local services between Watford and London Euston, plus Silverlink Metro services, are unaffected.
The checks were described as "precautionary", with the company saying: "At this point in time we are awaiting further technical detail and opinion before deciding how the trains can be returned to service."
Bus replacement services will operate along the affected route.
Virgin Trains will also collect Silverlink County customers every half an hour from Rugby, Milton Keynes and Watford to Birmingham and London.
The statement added: "In addition (Virgin Trains) will accept Silverlink County customers holding Silverlink only tickets on their trains from Milton Keynes and Watford, whilst Thameslink Rail and Chiltern Rail will accept Silverlink County customers on their trains as well."
Alan Bray, Silverlink representative, described the situation as a "major disruption".
He estimated that the fleet was made up of abut 30 321 electric multiple train units each comprising four carriages. More than 300 commuters use each service during the rush hour.
Mr Bray said: "For Northampton, Watford and Milton Keynes stations to London we take the vast majority of commuters to work."
He added: "There's no suggestion of any vandalism or terrorism threat. It was purely a precautionary examination of several of the trains overnight."
Of the safety problem discovered, he said: "We're waiting for technical detail and opinion before we can release that information or indeed find out how and when we can get our trains into service.
"The fault was found on several of the trains' brakes. We took the entire fleet out. Safety is our main concern."
Most of the trains are stored in sheds near Bletchley and inspectors will be carrying out checks today.
Silverlink staff were being posted outside stations to advise travellers on alternative routes.
Silverlink belongs to the National Express Group which is the largest operator of train franchises in the UK.
First Great Eastern, which uses the same model, said inspectors would also be examining their trains following Silverlink's decision.
A spokeswoman said: "As a precaution, they're looking at our 321s today. They will make a decision later today. We're looking at the possibilities."
First Great Eastern uses the 321 model on its mainline route from London's Liverpool Street to Ipswich and to Southend.
Peter Rayner, expert in railway operation and safety, called for companies such as First Great Eastern to carry out stringent checks.
"Withdrawing the service is a sensible precaution. There are precedents for that," he said of Silverlink's move.
"They are managing to work with other rail companies – it's a sign that they're pulling together."
He added: "It's important that not just one company does it but anybody operating the 321 class does it as well."
A spokesman for the Health & Safety Executive said they fully supported Silverlink's "precautionary" decision to remove the rolling stock from service.
A spokesman said: "We are working with them to find the root cause of the problem. We have an inspector at their Bletchley maintenance depot right now and we will be assisting to get the rolling stock back in service as soon as possible.
"I imagine in time there will have to be an investigation to see why this problem wasn't picked up earlier but the main task at the moment is to assist Silverlink."
He said that they were only told of the decision at 6.30am today, after Silverlink workers discovered "loose bolts" - which secure the brake disc to the train - during a routine inspection.
"They found one train set with loose bolts and then found others when they investigated further. Silverlink took the decision to take them out of service and then informed us."
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