The Department for Transport issued bids from three consortia which have been shortlisted for the project. Electric trains must be between 27 and 40 per cent more energy-efficient than those they replace, according to the specification.
Diesel trains must be between ten and 35 per cent more efficient, it adds. Lighter trains will help improve efficiency and reduce wear and tear on the tracks, the government said.
The replacement trains will be needed from 2015. The East Coast and Great Western main lines are set to be the first to benefit from the more modern carriages.