Virgin has pulled a number of its Voyager trains out of service today as it carried out safety checks on the entire fleet.

Maintenance workers discovered a problem with the transmission systems on the undercarriages of some of the trains last night.

Lee West, spokesman for Virgin, said about 30 per cent of services were not running, but the situation should improve later in the day.

Virgin has 78 high-tech Voyagers, which were introduced last year. An estimated 13 were affected today, Mr West said.

There are no Virgin cross country trains running beyond Plymouth to Cornwall and also none running north of Edinburgh.

Services from Birmingham and Manchester, Scotland, Plymouth and Bournemouth have been reduced from every half hour to every hour.

Mr West said the problem was discovered by maintenance company Bombardier Transportation as they carried out routine checks overnight.

''They identified a potential problem with the transmission system, which is part of the undercarriage.''

He added: ''Both Bombardier and our engineers are looking at it. What we have been doing is very much precautionary.

''If we find a problem we've got to put safety first.

''At least 70 per cent of our services are running. It may well be more by the end of the day.''

Mr West was unable to estimate how many Virgin passengers would be affected by the temporary timetable.

''We apologise for the unexpected disruption to our passengers and would like to assure them that their tickets will be valid on all our train services and with all other operators,'' he said.

Extra carriages were being introduced on some routes. The problem is not affecting Virgin West Coast services, which run from London's Euston station.

Virgin confirmed that engineers had discovered a fractured bolt on the transmission system of one of the Voyagers.

The flagship fleet, which cost Sir Richard Branson's company £390 million, has faced a series of setbacks since it was fully brought into service in September 2002.

The 125mph Voyager diesel trains were introduced in the hope of drastically reducing journey times on busy Virgin's CrossCountry line which runs through the North Yorkshire and the North-East.

They were also aimed at doubling the number of passengers using the cross-country routes.

But the fleet of 78 was unable to cope with passenger demand, with customers having to contend with overcrowding, as well as cancellations and technical faults.

Old style InterCity 125 trains had to be used to boost the service.

Each seat on the Voyagers has airline-style audio entertainment and each train boasts an on-board shop rather than the old-style buffet car.