Former prime minister Tony Blair has criticised the prison policies being pursued by the coalition government.
Mr Blair told the Daily Telegraph he "profoundly disagrees" with the approach adopted by Justice Secretary Kenneth Clarke.
Mr Clarke has outlined a "radical" shift from jail sentences to more community-based punishments to focus on rehabilitation and save money.
More than 85,000 people are currently in prison in England and Wales.
The justice secretary said he wants to "shut the revolving door of crime and reoffending".
New measures will involve paying private firms and voluntary groups according to how many prisoners they rehabilitate.
In a speech in June, Mr Clarke said prison had too often proved a "costly and ineffectual approach that fails to turn criminals into law-abiding citizens".
The justice secretary said that he would have regarded it as "impossible and ridiculous" when he was home secretary in the 1990s if someone had told him that by 2010 the prison population would have doubled to more than 80,000.
But in an interview with the Telegraph, Mr Blair said there was a need to imprison "those who deserve to be there".
The former prime minister said "dysfunctional families who produce 14-year-old kids stabbing one another to death" are "making people's lives hell" and suggested Britain could learn from developing countries which "just don't accept" criminality.
Mr Blair's comments amount to his first direct policy assault on the coalition since David Cameron won power from Labour in May.
The former prime minister, who recently published his memoir, once famously promised to be "tough on crime and tough on the causes of crime".