The package emerged as ministerial sources said the Government would not bail out the flagship pounds 580m Thameslink 2000 rail project, linking towns in the Home Counties north of London to the Sussex coast, which has been hit by the 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.
The pounds 300m Eurorail offer would be spent on lines used by Connex South Eastern trains in Kent, according to documents seen by The Independent, knocking between "eight and 12 minutes" off journey times to the capital.
Eurorail - a consortium of Kvaerner, BICC, NatWest and Seeboard - last week offered to take over the project, but indicated its completion would be delayed for four years and require pounds 2.3bn in public subsidies.
The company's proposals would see the 68-mile link end at a new terminus at St Pancras, but would put back the opening until 2007. Eurorail would not start building the link or seek to raise private finance until Eurostar passenger services were making money, which could take four years. Eurostar is currently losing pounds 180m.
The future of the rail link was thrown into disarray earlier this month when London & Continental Railways (LCR) said it could not complete the project without an extra pounds 1.2bn in subsidies. LCR's plans would have cut about 25 minutes off the 65-minute journey time into London for commuters from outer Kent.
About pounds 50m of the pounds 300m Eurorail "sweetener" would be required to straighten out tracks around Swanley, near the M25 motorway. The documents also said the offer might require the compulsory purchase of land at Herne Hill in south London and the demolition of some homes.
Another sticking point for the proposals is that it may disrupt existing rail services - which would mean that train operators would need to be compensated for delays.
The Thameslink 2000 scheme will speed up journeys between commuter towns of Bedford, Peterborough and Kings Lynn and those south of London, such as Brighton and Ashford.
Railtrack, the company building Thameslink 2000, said last week that the pounds 150m bill for the new station under King's Cross would have to be paid by the Government. But ministers have now made it clear to the company that new cash will not be forthcoming.
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 cheaper if it did not need to include facilities for Eurostar.