The ruling, which contradicts previous judgments made by the Home Office and the lower courts, was made in three test cases. It could potentially affect hundreds of others.

The Home Office said it was considering the ruling.

The BBC's Amanda Harper: "The Prosecution were challenged by articles in the Geneva Convention"

Two senior judges ruled there had been a breach of the Geneva Convention relating to the status of refugees. Article 31 of the convention says asylum seekers should not be penalised for entering a country illegally.

Lord Justice Simon Brown said: "It must be hoped that these challenges will mark a turning point in the Crown's approach to the prosecution of refugees for travelling on false passports."

Prison sentences

The landmark ruling follows complaints from immigration lawyers that hundreds of asylum seekers were imprisoned in the UK every year for using forged documents.

Many have received prison sentences of betwee six and nine months, higher than some people convicted of actual bodily harm, indecent assault or burglary.

Lord Justice Brown rejected Home Office claims that Article 31 obliged a refugee to claim asylum "where first he may". He ruled that any "short term stopover en route to an intended sanctuary cannot forfeit the protection of the Article".

The ruling is another blow for Jack Straw

The judgment follows a ruling last week that Home Secretary Jack Straw was not entitled to deport asylum seekers to France and Germany on the assumption that they were "safe" third countries.

The three test cases involved:

• Chouki Adimi, 31, who fled an Islamic terrorist group in Algeria and arrived at Heathrow airport via France with a false Italian passport and identity card.

• Dylan Sorani, a 27-year-old Iraqi Kurd accountant, who fled from northern Iraq in 1997. He said, with support from the Medical Foundation for the Care of Victims of Torture, he was tortured by the Iraqi authorities.

  He flew from Istanbul to Heathrow on a false Greek passport and was then provided with a false Dutch passport, but was stopped by airline officials while checking in for an onward flight to Canada.

• Astrit Kazui, a 27-year-old Albanian, was a bodyguard to President Sali Berisha and fled the country following the president's fall from power in 1997. In December 1998 he and his 20-year-old wife fled to Greece on false Greek passports and then came to England, intending to travel on to Canada to claim asylum there.

In each case, the asylum-seekers were prosecuted and jailed for up to six months for travelling with false documents. They all submitted claims for asylum, and were awaiting the results.

Anne Owers, director of campaign group Justice, said the ruling was "very significant in reinforcing the obligations of Britain to refugees under Article 31".

Nick Hardwick, chief executive of the Refugee Council, welcomed the ruling, and said: "It is a tremendous victory for asylum-seekers in the UK.

"We urge the government to now focus on the true task at hand, which is to create a fair and efficient asylum system."