Eurostar, the high-speed train company, is bidding to operate a key London to Scotland rail route, in a joint bid with French firm Keolis.
The successful bidder for East Coast, which has been operated in the public sector since 2009, is expected to be announced in October 2014, with the new franchise starting in February 2015.
East Coast has been run under the control of the Department for Transport since November 2009 after National Express pulled out, with its return to private ownership facing fierce opposition from Labour and rail unions.
Mick Whelan, general secretary of train drivers' union Aslef, said: 'It's shameful that a Government that fears it will lose the next election is tripping over itself in its rush to re-privatise a successful public service. Passengers, staff, and the taxpayer are all set to lose out."
Eurostar would take a minority share in the Keolis-Eurostar deal. Eurostar chief executive Nicolas Petrovic said: "By joining forces with Keolis, we bring a unique blend of expertise and innovation with a fresh perspective.
"The East Coast franchise is a vital economic artery and a key route for both business and leisure passengers which represents an exciting opportunity for future growth and investment."
Keolis, which is majority owned by French rail company SNCF, operates four UK rail franchises - Southern, Southeastern, London Midland and TransPennine Express.
Keolis UK chief executive Alistair Gordon said: "I believe that our ability to draw upon an international track record of delivering complex long-distance services, coupled with Eurostar's reputation for customer excellence, is a unique proposition."