A leaked proposal to bring back a three-tiered system on East Coast Main Line Trains has angered rail union leaders and the Labour Party.
Unions accused the government of re-privatising the line which has been in state hands for four years.
According to the Daily Mail, the Rail, Maritime and Transport union (RMT) said it had seen a copy of the prospectus for returning the East Coast Mainline to a private operator by early 2015.
The document allows bidders to establish an "intermediate class between Standard and First", which could mean the return of three classes of travel, which was last seen on Britain's railways in 1956.
According to the Independent, Eurostar and Virgin Trains have both expressed interest in the East Coast franchise.
Labour's shadow transport secretary, Mary Creagh, said: "David Cameron says we're all in this together but if that's true then why is he going back to the 1950s and reintroducing Third Class?"
But a Department for Transport spokesman told the BBC: "This is ill informed scaremongering from the RMT.
"By choosing to release inaccurate information, they are misleading the public. We have no intention of requiring a 'third class' service, reducing performance levels, or in any way devaluing this vital railway."
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