Downing Street has rejected suggestions Tony Blair's decision to look again at sentencing is a sign of panic.
Home Secretary John Reid earlier this week denounced the case of a paedophile who could be freed within five years.
Further revelations that 53 offenders given life sentences were freed within six years prompted Mr Blair to promise new legislation on sentencing.
No 10 says a review is under way but Mr Blair was urged to stop tinkering by the ex-chief inspector of prisons.
Lord Ramsbotham said the prime minister should stop making changes to the legal system, saying they caused more problems than they solved.
"I just wish he'd shut up, frankly," he told BBC Two's Daily Politics show.
Meanwhile, Lord Chancellor Lord Falconer has defended judges, saying they should not be the "whipping boys" for a flawed system.
Lord Falconer, who is a Cabinet minister, said there needed to be a "very urgent" look at the automatic discounts given on jail terms as a reward for guilty pleas.
The issue was raised by the case of paedophile Craig Sweeney, who was jailed for life at Cardiff Crown Court this week but could be released in five years because he pleaded guilty.
Although Judge John Griffith Williams QC imposed an 18 year sentence, a one third discount for pleading guilty, plus a year already spent in custody, meant he would be considered for parole in five years.
Lord Falconer told BBC Radio 4's Today: "Everybody agrees the sentence isn't what we wanted but it wasn't the judge's fault.
"One of the problems that there has been recently is announcement after announcement from the prime minister that he's going to do this and that and the other, and more people are going to come in [to jail] for longer.
"Unfortunately all that's doing is crowding the system even more that it is."
The furore over who was to blame for Sweeney's relatively short sentence was stoked when the home secretary described it as "unduly lenient".
That prompted an angry response from Attorney General Lord Goldsmith, who feared it might appear that he had political motivation if he asked the Court of Appeal to considered lengthening the sentence.
Asked about Mr Reid's intervention Lord Falconer, whose job includes the defence of the independence of the judiciary, said: "John Reid is perfectly entitled to say 'I think the sentence is too low'. He did not attack the judge."
However, shadow attorney general Dominic Grieve criticised Mr Reid, calling for him to apologise for his remarks.
Mr Grieve told BBC Radio 4's Today programme "there was no justification" for the home secretary's comments.
"The sentencing exercise that the judge carried out was entirely the result of the government's own 2003 Criminal Justice Act; he followed it to the letter."
Lib Dem home affairs spokesman Nick Clegg said public confidence was vital to the operation of the criminal justice system.
He said many sentences currently called "life sentences" were clearly not for life so should be renamed. Only cases where someone was to genuinely spend their entire life in prison should be called life sentences, he said.