Some murderers are serving too long in jail, meaning prisons will become "full of geriatric lifers", Lord Chief Justice Lord Phillips has said.
The government wants mandatory life sentences for murder to stay
He questioned the need for a mandatory life sentence for murder and voiced doubts murder law reforms would succeed without changing the sentencing regime.
The prime minister's official spokesman has dismissed his comments.
Lord Phillips, who is the most senior judge in England and Wales, made his remarks during a speech in Birmingham.
Speaking at the University of Birmingham on Thursday, he said it was regrettable that government guidelines on the length of time murderers should spend in prison had the effect of "ratcheting up" sentences.
He also said he was "not optimistic" that the Law Commission's recent proposals to create two categories of first-degree and second-degree murder would work.
The Criminal Justice Act 2003 requires courts in England and Wales to impose mandatory sentences for any of 155 offences under certain circumstances.
The Act also sets out guidelines on minimum jail terms for people sentenced to life for certain categories of murder. In Scotland judges are left to set minimum terms themselves.
Prime Minister Tony Blair's official spokesman said the government recognised that the Lord Chief Justice took this view, but added: "We believe that people should be kept in prison as long as they are judged to be a danger to society."
According to the Home Office, there were 2,190 prisoners aged over 60 in England and Wales as of December 2006.
In 2005, Lord Phillips' predecessor, Lord Woolf, said he opposed Parliament passing laws that forced judges to impose particular sentences.
Previously, Lord Phillips has spoken out on a number of key issues, including his concern about prison overcrowding and the need to make greater use of community sentences.
'Grave and devastating'
Norman Brennan, director of the Victims of Crime Trust, said Lord Phillips had "taken leave of his senses".
He added: "When some murderers serve as little as eight years for such a grave and devastating crime, it makes a mockery of the lives of those who have been murdered."
Lyn Costello, of pressure group Mothers Against Murder and Aggression, said parents of murder victims would be "heartbroken" by his comments.
The Daily Telegraph's legal affairs editor Joshua Rozenberg said Lord Phillips' remarks reflected a general mood among the judiciary that mandatory sentencing had tied their hands.
However, John Suffield, whose son John was killed in 1981 during a robbery in a Liverpool betting shop, accepted prison must be about rehabilitating offenders.
He told BBC Radio Five Live his son's killer had served nearly double the minimum term and should be released.
Sir Louis Blom-Cooper QC, a former chairman of the charity Victim Support, told the BBC's Today programme that Lord Phillips' intervention was "entirely welcome".
He added: "All his predecessors have been very vociferous about the mandatory sentence being wholly incompatible with a modern civilised penal system."
Juliet Lyon, director of the Prison Reform Trust, said new guidelines and the introduction of indeterminate terms meant prison sentences were "far tougher and far harsher" than 10 years ago.
She said: "The use of mandatory sentences do not give judges discretion to consider each case that comes before them on an independent basis."
Statistics show that some 10% of the prison population in England and Wales - about 8,800 people - are serving life or indeterminate sentences.
"That's more than all those in Germany, France, Italy and Turkey put together," Ms Lyon said.