Ministers are expected to announce the delay soon after the deadline for the original London & Continental Railways (LCR) consortium to re- bid for the project expires this Friday.
The extension would allow other bidders - such as Railtrack - to come forward with new proposals, although it is understood that they may have to reform under the LCR name to avoid the Government having to re-tender the entire project. Going through the entire bidding process again would effectively scupper the rail link.
The future of the rail link was thrown into disarray earlier this month when LCR said it could not complete the project without an extra pounds 1.2bn in subsidies. The original LCR plans would have cut about 25 minutes off the 65-minute journey time into London for commuters from outer Kent.
Alastair Morton, the Government's adviser on the CTRL, is understood to be considering more than 30 different scenarios under which the high- speed line linking the Channel Tunnel and central London could be built.
One option would see the 12-mile tunnel from east London scrapped and instead a new fast service using the North London line run from Stratford. This would require some overland work to be done to allow trains to run to St Pancras, the central London station, but cutting out the tunnelling costs would save nearly pounds 1bn.
Another plan - put forward by the contractors Bechtel and Ove Arup, currently members of the LCR consortium - would see the link built in two phases with the line to Waterloo completed first and the link to St Pancras finished later.
The whole project could then be sold off to Railtrack. The owner of the link would recoup its costs by charging large access fees to Eurostar.
Civil servants at the Treasury also believe that many individual bits of the project could be parcelled off to the private sector. They point out that the building giant Blue Circle is poised to build a pounds 2bn office and residential complex at Ebbsfleet, north Kent - with the proposed Eurostar terminal at its heart. This new station and some of the railway line required, say Treasury mandarins, could be sold off to Blue Circle - thus reducing the cost.
The flagship pounds 580m Thameslink 2000 rail project, linking towns in the Home Counties north of London to the Sussex coast, is likely to suffer from CTRL's collapse.
Thameslink 2000, which will improve services for cross-London commuters, was relying on the pounds 5.4bn CTRL project to build a pounds 150m station underneath King's Cross.
As a compromise the proposed station - which was to offer an interchange between the Underground, Eurostar and mainline services - is likely to be scaled down.
Sources close to the project said that the station could be built much more cheaply if it did not need to include facilities for Eurostar.Reuse content