Ryanair-style railway carriages may loom for passengers on the East Coast main line with another Con-Dem hint at the return of third-class travel.

MPs are due today to debate the coalition's plans to put the publicly owned London-to-Scotland service back up for sale just four years after it rescued the route from debt-ridden privateer National Express.

An eyes-only circular for the route's bidders leaked last month proposed a new "intermediate class between standard and first" as part of the new franchise.

Tory Transport Minister Stephen Hammond sought to play down the paper, telling MPs last week his department had "no intention of requiring" a three-class system.

But neither would they rule it out, he continued.

"Bidders are however free to consider such initiatives where they meet the overall requirements of the department's specification," he said.

Rail union RMT general secretary Bob Crow urged opposition MPs again to fight the state sell-off in light of the admission.

"Not only is the government prepared to rip apart the successful publicly owned East Coast service but it is opening the door to the private sector to create a new, third class of service.

"Although they won't specify exactly what that means, 20 years of experience of private rail operators points to a Ryanair model with passengers rammed in to creaking cattle trucks with a surcharge for everything from your bags to using the toilets.

"The reprivatisation of the East Coast can and must be stopped and it should be used as a platform from which to launch the full renationalisation of Britain's railways," he said.

The debate also comes just weeks after the route's state-owned operator reported more than £200 million in returns to the taxpayer.

In October Directly Operated Railways reported annual revenues of £208.7m from its sole charge East Coast.

In May Department for Transport figures showed the taxpayer spent just half a penny in subsidies for every mile travelled on the East Coast Main Line.

The average rate of subsidies among its free-market rivals was 10p per passenger mile - a rate 20 times more costly than East Coast's operation.