Train builders will be urged by the government to find ways of fitting more passengers into each carriage on long-distance trains as it prepares to publish its ideas about what should replace the ageing InterCity125 fleet.

The requirement is one of several stipulations in tender documents apparently aimed at restraining the cost of a replacement for the workhorses of several of Britain's long-distance rail routes. The Department for Transport is thought to want more seats in each carriage in order to secure a 20 per cent increase in passengers.