BBC's Andrew Hoskin: Union warns that this could derail Home Office plans

Mr Straw is holding urgent talks with his French counterparts to try to stop the flood of asylum seekers from the former Yugoslavia using the so-called "two-ticket scam".

Straw: Talks with French counterpart

He warned that unless tough action is taken by the French, he will start fining Eurostar £2,000 for every illegal immigrant caught coming off trains from Paris.

Immigration Minister Barbara Roche told the Today programme on BBC Radio 4: "We have made it perfectly clear to the operating company that if we can't find an acceptable solution we will have to think about legislative means,"

Ticket scam

Under the scam, illegal immigrants buy two train tickets in Paris - one for Calais and the other for London.

When questioned by French border police on board the train, they show the ticket for Calais and are therefore not asked for their passports.

At Calais they stay on the train, switching to their London tickets.

Immigration Minister Barbara Roche: 'Government will act firmly.'

Officials on the train assume they have already had their passports checked.

Once they arrive at Waterloo, they claim asylum - a process which can take years and during which time they can live in Britain.

The Home Office said British immigration staff had caught 1,320 would-be illegal immigrants from the former Yugoslavia in June - almost double the number from the same month last year.

A rising number were also coming to Britain from Somalia.

'Worrying rise'

A Home Office spokeswoman added: "The number of undocumented and improperly documented passengers using Eurostar to travel to the UK is particularly worrying.

"We are in urgent discussions with the French authorities about the problems and are examining a number of options with them.

"These include UK immigration officers operating controls at Eurostar stations in France.

"We have made it clear to the French that unless an effective solution is found, we will not hesitate to use the civil penalty measures introduced in the Immigration and Asylum Bill, which will enable us to charge French railway operators £2,000 per person if they continue to bring in improperly documented passengers."

The government already fines Eurostar for illegal immigrants brought in from Belgium, but French law prevented the fines being extended to those coming from Paris.

The new Immigration Bill currently going through Parliament closes this loophole by referring to the fines as "civil penalties".

It will also extend the fines to lorry drivers who bring in stowaways in their cargoes. It is expected to become law by November.