David Cameron has called for a junior Home Office minister to be sacked, saying her handling of the foreign convictions row showed she was little more a "giant franking machine signing letters".
The Conservative leader was referring to Joan Ryan, who it has emerged was informed months ago that details of 27,000 Britons convicted abroad since 1999 had not been put on the police database, but did nothing to tackle the problem.
"Last week the junior Home Office minister responsible told us she knew nothing about the fiasco of the foreign criminal records," Mr Cameron told a heated session of prime minister's questions in the Commons.
"Now we know she was receiving and signing letters about the issue as long ago as October. Why is she still in her job?"
Tony Blair defended the minister, saying although the Association of Chief Police Officers (Acpo), which took over the handling of the convictions database in May, had told her about the problem, she was unaware of the scale of the backlog.
But Mr Cameron said: "The prime minister's defence seems to be that the minister knew about the problem but not about the backlog. But the problem was the backlog.
"Don't you want ministers who are going to ask some questions and show some judgment rather than acting like giant franking machines signing letters?"
The prime minister responded: "It simply is not correct to say that the problem was the backlog alone. The problem was that there was no proper system and hadn't ever been a proper system for the exchange of information between European countries."
Since May last year, details of convictions have been automatically shared between European Union member states. Mr Blair said the new system was working, adding Acpo not found any serious problems when checking the backlog of cases before then.
He refused Tory requests to publish the letter sent to Ms Ryan last autumn, saying it would be made public after Home Office permanent secretary David Normington carried out his review into the affair.
But Mr Cameron said: "This inquiry is being carried out by the head of personnel at the Home Office - if this scandal had been conducted in a care home in a hospital or in any business in this country, do you think you would ask the head of personnel to conduct the inquiry?"
He added: "Doesn't it show this government and these ministers are interested in protecting themselves and not in protecting the public?"
The Tory leader finished by attacking Mr Blair over another Home Office scandal - news that a third terror suspect who was under a control order has gone on the run. But the prime minister seized the opportunity to have the last word.
"Let me just remind the honourable gentleman that it was the desire of this side of the House to detain people [suspected of terror offences rather than put them under control orders]," he said.
"We were the government that introduced legislation toughening up the laws on terrorism that he and his colleagues voted against. So the one group of people we will not take lessons from on control orders and action on terrorism is him and his colleagues."