This was several days after his photograph had been published widely in newspapers and on television. Hussain Osman escaped abroad on a Eurostar train last Tuesday en route to Rome, where he was finally arrested by Italian police on Friday.

His British passport was checked only by French immigration officials at Waterloo because outgong British passport checks were abandoned at the station last year. Yesterday reports in Italy suggested that Osman, who was born in Ethiopia, used fake Somali documents to obtain political asylum in Britain about five years ago.

Osman, who has also used the name Hamdi Isaac, previously lived in Italy with other members of his family and speaks fluent Italian. It is not known if he attempted and failed to obtain Italian citizenship before travelling to Britain to claim asylum.

The Italian interior ministry said Osman, who lived in London with a girlfriend and three children, had an Italian residence permit that had expired in 1996. On the form he had specified his nationality as Ethiopian. Ethiopians are not normally eligible for asylum in Britain.

Last year the Home office admitted it had a problem with citizens of other African countries claiming Somali nationality and introduced language tests to stop the fraud. The changes were made amid condemnation of Britain's lax immigration controls. However, Osman had already illegitimately obtained his British passport under the lax system.

David Davis, the shadow home secretary, said: "This demonstrates the vital and immediate necessity for the government to get a grip on our porous borders, both in terms of people coming into the country and in terms of people leaving."

Concerns are being raised as to how Osman was able to leave the country amid a massive manhunt. After the July 7 attacks and the attempted bombings a fortnight later, the police elite Special Branch unit was supposed to be monitoring the Eurostar terminal. British immigration officials were also making spot checks on certain passengers.

Yesterday the Home Office refused to comment on security lapses or to reveal what information had been given to French officials at Waterloo. Officials are understood to be urgently retrieving Osman's immigration records but Charles Clarke, the home secretary, is on a long vacation in New England and therefore unable oversee inquiries into the alleged failings of the immigration service.

A senior police source said that the Eurostar terminal was "plastered" with pictures of the men. He alleged that French and British immigration officials were to blame for letting Osman slip through.

"This shows the controls were fairly weak," he said. "This man's photograph, like that of all the suspects, was plastered all over Waterloo station, including at the Eurostar terminal.

"The French officials there can be a little difficult at times. It's just their attitude. It's the French way, slightly arrogant."

A police spokesman said the CCTV image of the Shepherd's Bush bomb suspect, whose identity was not known when he left the country, was the least clear of the four. A better image was released only last Thursday, after he had left the country.

The suspected bomber’s successful escape will lead to renewed calls for a tightening of security controls at Britain’s borders.

Passport checks for European Union passport holders leaving Britain were abandoned in 1998, saving the government just £3.5m annually.

Airlines and ferry companies still have to check passengers’ passports, instead of immigration officials. When British immigration withdrew from making checks last year for Eurostar passengers, it failed to pass on the obligation to the company.

John Tincey, vice-president of the Immigration Service Union, said: “The checks at Waterloo are made by French officers working for the French government.

“Their job is to look out for French interests. In practical terms, they may not have been looking for him (Osman) so hard.”

Osman is thought to have travelled to Paris where he then took the Métro to another mainline station and caught a train to Rome, which made several stops in northern Italy. His journey through Europe is leading to pressure in other European countries, particularly Italy, for border controls to be reintroduced.

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