The line has been under threat since the builders, London and Continental Railways (LCR), ran into financial problems earlier this year.

Richard Hope, from Railway Gazette: second phase of the link is the key (2'09")

The Deputy Prime Minister, John Prescott, is due to give a Commons statement on a rescue package including an extra £700m in subsidies for the link.

LCR asked for £1.2bn in January when the full extent of its problems came to light but Mr Prescott told parliament he had rejected a request to lend the company any extra money.

John Prescott: refused a first request for cash in January

Some £1.8bn of public money is already committed to the line which is costing £5bn in total, and will now be built in two stages.

The first from Folkestone to Ebbsfleet in north Kent would mean a reduction of 15 minutes on journey times into the existing Waterloo International station.

The second stage is the more expensive, as it requires a 12-mile tunnel under Barking and Stratford in east London before the final stage to a new terminal at St Pancras.

Richard Hope, consultant editor of Railway Gazette, said he expected Railtrack to commit itself to the first stage, but not the second. This could mean a further delay.

"We shall see the first part open - probably in 2003", he predicted. But he added: "I would think we're looking at another four or five years at a minimum before Eurostar arrives at St Pancras."

He said the link was important to reduce the journey time so Eurostar could compete more effectively with airlines.

It would also mean better connections for railway stations serving the Midlands and the North.

Lib Dem transport spokesman Matthew Taylor predicts "absolute chaos" (2'29")

But Liberal Democrat transport spokesman Matthew Taylor was more pessimistic about the second stage.

"It's very hard to believe it will ever be built", he said.

If that happened he predicted "absolute chaos" on commuter lines in south-east London, with either Eurostar unable to run trains in the rush hour, or commuter services having to be cancelled to make way.

Tory councillor Mike Claughton says announcement is long-awaited for people in Kent (25")

However, people in Kent are likely to welcome news that the route of the first stage will finally be decided.

Mike Claughton, a Conservative councillor in Ashford, said the announcement would "rid people of the suffocating blight which has effectively choked their lives".

The entire link, which would carry trains at 300kph (186mph) through south-east England promises to reduce the journey time between London and the Continent by up to 35 minutes.

The tunnel: fast but trains have to hit the brakes in England

Trains now rarely travel faster than 80mph on the crowded Kent tracks they have to share with commuter services.

The top speed is reached in France and Belgium on fast links from the tunnel to Paris and Brussels.

The French link was publicly funded and opened on schedule along with the Tunnel in 1995, with the Belgian line opening last December.

In his statement to the Commons Mr Prescott is also expected to give details of who will take over the running of the Eurostar service.