Major changes may have to be made to the new electric Japanese bullet trains being built for the Great Western Railway.
Electrifying the line is now so late and over budget diesel engines look set to be fitted so they can start running on time in two years.
A report into the impact of the late running project is due next month.
The delay means the electric overhead lines will be late so the only way to stop them staying in the sidings and going nowhere is to put diesel engines on them adding millions to the cost so they can run.
The trains are costing £5.8 billion and are being built by Hitachi. The electrification cost of the line has tripled from £547 million to £1.7 billion.
The Government say some trains were always going to be able to run on both electricity and diesel but critics say many more will have to be fitted with the engines.
?The new trains are part of the Intercity Express Project that will see new fleets of trains on Great Western and the East Coast. They will run from Paddington to Berkshire, Oxfordshire and Wiltshire.?
The trains are at the centre of a row with the RMT union who are unhappy at the removal of buffet cars. There have been five days of strike action in protest.
GWR say it will allow for extra seats to help overcrowding and there will be a trolley service to provide catering.