Tony Blair and David Cameron have clashed over the 53 criminals sentenced to life who have been freed after serving less than six years in prison.
The judge acted in accordance with guidelines in sentencing Sweeney
During stormy Commons exchanges the Tory leader blamed laws introduced by Labour for the convicts being freed.
The prime minister accused Mr Cameron of talking "rubbish" but said new measures were being prepared.
He insisted laws passed in 2003 meant fewer prisoners were now given parole mid-way through their sentences.
The Criminal Justice Act allowed judges to jail more serious offenders for indefinite periods.
The clash at prime minister's questions followed the news 53 people sentenced to life since 2000 in England and Wales have already been released on licence.
This week paedophile Craig Sweeney got life but could be out in five years.
The Sweeney case prompted Home Secretary John Reid to call the sentencing "lenient".
The Home Office is now promising a "further strengthening" of the rules governing prisoners' release. Downing Street later said legislation was liekly to be published by the end of next month.
Better than the last?
In the Commons Mr Cameron said: "In the last 40 days the new home secretary has been hard at work.
"He has potentially undermined his department's own deportation proceedings, he's shelved his own anti-crime campaign at the last minute, he's misled the public over the employment of illegal immigrants in his own department and now he has criticised judges for their implementation of new Labour law."
Mr Blair rubbished Mr Cameron's claims, saying that when the "Criminal Justice Act came before this House, the Conservative Party voted against it".
The Tories "talk tough in the media, they vote soft in Parliament", he said.
Earlier, Monmouth Tory MP David Davies whose questions revealed the release of the 53 lifers, said: "Members of the public are being led to believe that once caught and found guilty, these criminals are being sent to prison to serve out the whole of their sentence. They are being misled."
But a Home Office spokesman said: "Tariffs are set by judges and release is by order of the parole board.
"The most common offence represented among the 53 is grievous bodily harm."
The spokesman added that 500 people a year had received life sentences since 2000.
Lib Dem home affairs spokesman Nick Clegg said: "Public confidence is vital to the operation of the criminal justice system, and releasing inappropriate prisoners could be another blow to an already beleaguered system."
It was a "huge surprise" to many members of the public that lifers were released at all and it was time to re-examine the labels that were given to sentences, said Mr Clegg.
Judge John Griffith Williams QC was acting in accordance with guidelines when he sentenced Sweeney, 24, at Cardiff Crown Court.
Sweeney - who was known to the family - had snatched the girl from her home after she had returned home from a shopping trip and while her mother made a telephone call.
He drove her to his Newport flat where he was living after being released early from a three-year sentence for indecently assaulting a girl aged six. There she was sexually assaulted.
Earlier this month, five judges at the Court of Appeal increased the minimum jail sentence on Alan Webster, convicted of raping a 12-week-old baby, after the case was referred to them by the attorney general.