Tony Blair and Iain Duncan Smith have accused each other of being soft on asylum and the war on terror.

The Conservatives have called on ministers to do more to vet those seeking refugee status after a number of police anti-terror raids leading to the arrest of asylum seekers.

Labour, in turn, has accused Tories of blocking the tough laws needed to do the job.

During heated Commons exchanges, Iain Duncan Smith attacked asylum rules that allowed a former Taliban fighter to claim refugee status under human rights conventions.

"How can the prime minister be so complacent when we discover that Taliban fighters that only a few months ago were trying to kill British soldiers are now living in Britain," he demanded.

"Countries across the world have the right to say no to those who want to destroy their freedoms and way of life, why can't Britain do so?"

Blair hit back by listing a series of controversial asylum and terror crackdowns.

"Britain can and should which is the reason why we introduced the measures in anti-terrorism legislation post-September 11 and the reason also for the Nationality Immigration and Asylum Act last year," he said.

"Let me again point out to him that when we introduced measures that said that any asylum seeker who is convicted of a crime should be deported those measures were weakened by Conservative amendments."

The prime minister criticised Oliver Letwin's opposition to legislation aimed at asylum seekers and terror suspects.

"I simply say to the right honourable gentleman that it is wrong for the Conservative Party to say this is a big problem, to call on us to deal with it and then to oppose the very measures necessary to deal with it," he told MPs.

"When we introduced measures in the houses of parliament there were Conservative peers, Conservative members of his own front bench who told us these measures were illiberal and contrary to civil liberties and we had to fight to get measures through."