All 13 of the company's east coast trains are being refurbished

The company, which won the mainline franchise in August 2007, says the improvements will make journeys greener and more comfortable.

New contoured seats, carpets, lighting and windows are being installed in carriages on all 13 high-speed trains.

The complete interior makeover is due to be completed by 2009.

Richard McClean, production director at National Express, said: "We are making good progress with the project to transform the popular 125 diesel trains.

"They have given fantastic service and in their new, much improved condition, will continue to set high standards for years to come."