Smash hit

Under the new policy, a Conservative government would not just pull Britain out of the Refugee Convention, but pull back from certain commitments in the European Convention on Human Rights.

The purpose of that move, Mr Howard said, would be to break the link between arrival in the UK and the asylum system, so that tens of thousand of economic migrants - mostly young men -would no longer have the incentive to abuse the system with the help of people-smuggling gangs. Instead, Britain would take a quota of genuine refugees allocated by the UNHCR from its resettlement camps.

Mr Howard added: "People will face a clear choice at the next election: unlimited immigration under Mr Blair or limited, controlled immigration with the Conservatives."

But Rupert Colville, a spokesman for the Geneva-based agency, warned that Britain's withdrawal from the Refugee Convention could create a "domino effect" that would bring the international asylum system to its knees. He said that if that system collapsed, the flow of asylum-seekers arriving in Europe might actually increase because it would be harder for refugees to find sanctuary in neighbouring countries.

"We think withdrawing from the Convention would be extremely counter-productive," Mr Colville told Times Online. "What kind of message would that send to other countries? What would happen if Tanzania said that, or Pakistan or Iran, which have had millions of refugees coming in to them?"

Mr Colville added: "Asylum figures in Europe are at their lowest in 17 years, the numbers are right down and in the UK they're down at an even greater rate than the rest of Europe, so it's a little hard to see why there should be such hyperbole."

The UNHCR spokesman described the delay in processing asylum claims as a "management issue" which was partially a hangover from the flood of refugees from the former Yugoslavia in the early 1990s. "The length of time it took to get through the system became so long that it became wide open to abuse. That's improved considerably in the last year or two," he said.

Mr Howard's policy was also attacked by human rights groups and by Trevor Phillips, chairman of the Campaign for Racial Equality, who said it was based on the "ill-informed propaganda of demented anti-immigration groups".

Critics of the policy pointed out that although net immigration is at around 160,000 a year as Mr Howard stated, the number of asylum-seekers, which hit a record 100,000 in 2002, has dropped by 40 per cent since then, to 60,000 of the overall total.

Shami Chakrabarti, the director of Liberty, a civil rights group, attacked Mr Howard's proposals. "Quotas are for cod fishing, not humanitarian protection. The Refugee Convention is one of the proudest legacies of World War Two," she said. "It is a little obscene to denigrate it as we approach Holocaust Memorial Day."

Mr Howard made clear that he was happy to see immigration and asylum feature as an issue at the general election, which is expected on May 5. He said: "People will face a clear choice at the next election: unlimited immigration under Mr Blair or limited, controlled immigration with the Conservatives."

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