By Simon Montague BBC Transport Correspondent

Rail bosses at Virgin admit train services on Cross Country routes are being badly disrupted by the effects of severe weather and new timetables.

Virgin's new fleet of Voyager and Super Voyager trains are facing "total disruption of maintenance schedules", caused by slippery rails, landslips and even rough seas.

A new timetable which doubled the frequency of services, but halved the length of trains, is also leading to serious overcrowding problems.

Passengers on Virgin's cross country routes, which stretch between Penzance and Aberdeen, have suffered delays, cancellations, packed carriages and alternative bus services.

Leaves on the lines

Virgin says slippery tracks caused by falling leaves have led to skidding when trains try to brake.

The skidding causes "flats" on the surface of wheels, forcing trains to be taken out of service for repairs.

Customers face more cancellations

Virgin is also modifying trains to overcome heavy seas which spray over the sea wall at Dawlish, in Devon.

Saltwater has affected electrical equipment on the roof of new trains, making the on-board computers shut down locomotive engines.

A new winter timetable has exacerbated the disruption caused by autumn weather.

Virgin has doubled frequencies on many cross country routes.

But it has introduced a 79-strong fleet of four or five car, Voyager trains, to replace the nine car, High Speed Trains which are being withdrawn.

Standing room

Some services are suffering serious overcrowding, with passengers complaining of standing room only for long journeys.

Virgin admits it is reducing the number of cheap, advance purchase tickets on some trains, to persuade passengers to travel at less popular times.

Passenger groups accuse Virgin of failing to provide enough luggage space on the new trains.

They say aisles are becoming blocked by bags and suitcases.

Virgin says there is plenty of luggage space, and staff are working hard to familiarise passengers with new storage areas, such as between seats.

Passengers have also complained of buffets and toilets being out of service.

Virgin says disrupted timetables and maintenance schedules are to blame.

Track upgrades

Failure to finish engineering work on time is adding to Virgin's difficulties.

Railtrack should have completed the upgrading of track between Wolverhampton and Stafford, increasing the line speed from 90mph to 110mph.

But the work may not be finished until Christmas.

Temporary speed restrictions are causing further delays.

Virgin has been forced to cancel numerous services, including 18 trains on Monday this week.

The company says it is cancelling or shortening a number of services, to try to improve punctuality over the next month.