The Government today signalled the start of the sale of High Speed 1 (HS1) - the 68-mile London to Folkestone Channel Tunnel rail link.
Likely to bring in around £1.5 billion, the sale could open up the route to more operators, including - possibly - overseas concerns.
At present, HS1 is used by the London to Paris and Brussels high-speed train company Eurostar and also by the Southeastern train company.
Southeastern operates London-to-Kent domestic services on the line, using Japanese-built Javelin trains.
The route is currently being run by London and Continental Railways (LCR) under the control of the Department for Transport.
Launching the sale at St Pancras today, Transport Secretary Philip Hammond said: "High Speed 1 is a national success story and a world-class railway operating to international standards. The money generated by this sale will make an early significant contribution to the crucial task of reducing the public sector debt.
"That's good news for the taxpayer. But the sale will also bring benefits to passengers as the successful private bidder will be incentivised to attract new operators serving new routes.
"This is part of the Government's approach to making our national assets - and every taxpayer pound - work harder. The Government does not have to run everything directly - we need to take prompt action where private enterprise can provide both a better deal and a superior service to the public."
Mr Hammond said he expected that the Government would be able to announce a winner of the HS1 bidding process before the end of the year.
HS1 runs from St Pancras station in London to Folkestone. Stations en route are Stratford in east London, Ebbsfleet in north Kent, and Ashford in Kent.
The successful bidder will become the owner of HS1 Ltd which has a 30-year concession to run the line and stations.
Following the sale, the performance of HS1 Ltd will be independently policed by the Office of Rail Regulation to ensure that rail passengers' interests are effectively safeguarded.
Mr Hammond today reiterated the Government's aim to link HS1 to HS2 - the north-south high-speed line that the Government hopes to start in 2015.
Bob Crow, general secretary of the Rail Maritime and Transport union, said: "We now have the clearest indication possible that this ConDem Government will flog off every public asset that's worth a few quid and that includes the Channel Tunnel Rail link.
"The message is clear - this Government are committed to cuts and privatisation in the time-honoured Tory tradition of Margaret Thatcher.
"RMT will launch an all out fight to stop the selling off of the last remaining publicly-owned fragment of our railway network and to keep it out of the hands of the profit-driven vultures from the private sector."
LCR chief executive Mark Bayley said: "HS1 is a unique and high-quality infrastructure business. A world-class railway, it speeds tens of thousands of people between London, Kent and continental Europe every day.
"In addition, the line has already led to substantial regeneration along the route and will play a vital role in transporting spectators to and from the London 2012 Olympic and Paralympic Games."
Anthony Smith, chief executive of rail customer watchdog Passenger Focus, said: "Passengers will not worry who is running the high-speed infrastructure as long as any competition works in the overall passenger interest, fares represent value for money and the quality of the stations is maintained.
"St Pancras, in the last national passenger survey, was the top rated of Britain's busiest stations."
Gerry Doherty, leader of the TSSA rail union, said: "The Tories should not be selling off the family silver so fast, especially when the taxpayer spent £5 billion building HS1.
"The coalition insists it is still committed to building HS2 between London and Scotland, again using public money. It makes no sense to have a private company charging extra for high-speed travel south of London while a public company runs high-speed travel north of the capital."