Tony Blair has challenged David Cameron to "put your vote where your mouth is" after enduring a barrage of criticism about the government's criminal justice record.
The prime minister said that while the Conservative leader could criticise the handling of the foreign prisoners row, immigration and human rights law, it meant nothing if he voted against the government's attempts to deal with the problems.
"I don't say we've got everything right, we've got to do more, but every time we introduce the tough measures he tells the media he wants, he goes out and opposes them. Perhaps next time we introduce them he'll put his vote where his mouth is," Mr Blair declared.
His comments came in another round of hostile prime minister's questions, when Mr Cameron took the opportunity once again to lay into the Home Office for its failure to deport and even locate former foreign prisoners.
In an effort to fend off criticism, Mr Blair announced two weeks ago that foreign criminals convicted of an imprisonable offence would from now on be automatically deported, but he has been forced to clarify this strong stance.
And home secretary John Reid this week said it would only be for people convicted of a "significant jail term", prompting Mr Cameron to ask whether the government really had a plan at all.
Mr Blair replied that if someone was convicted for a "very short period of time" and had been in Britain "for a long period of time" then the presumption of automatic deportation may not apply - but that still left "the vast bulk" of foreign prisoners.
But Mr Cameron told the Commons today: "I think he's making it up as he goes along. This is an example of a government in paralysis."
The Tory leader moved to the issue of the Human Rights Act, which he said had not been working properly for years, and cited the Home Office's admission that it does not know how many illegal immigrants are in Britain as yet another example of "paralysis".
"Why, after four home secretaries, 43 pieces of [criminal justice] legislation and nine years would anyone believe [the prime minister] is the man who can sort it out?" he asked.
But Mr Blair hit back, admitting that "he's right, it is necessary to control illegal immigration better", but saying one way to improve the system was to introduce ID cards - something the Tories had tried to oppose.
"If we want to track the identity of people coming in and out of this country, that is what we have to do and the truth is that he isn't prepared to do that," he declared.