When Mr Blair came to power in 1997 there were just over 60,000 prisoners in England and Wales and the prisons were overcrowded. As he leaves, the prisoner population is just over 80,000 and the prisons are still overcrowded. Almost 20,000 prisoners are held two to a cell designed to hold one.
The total number of prisoners in the whole of the UK is over 89,000. Previously it took nearly four decades, from 1958 to 1995 for the prison population to rise by 25,000. France, which has the same population as the UK, has only 52,000 people in prison, and Germany, a country with 20m more people than the UK, has only 77,000 imprisoned citizens.
The reason for this absurd disparity is not that there is more crime in the UK or more convictions in court. The number of people found guilty by the courts has been stable at around 1.5 million per year for the past 10 years. The main reason for prisoner population increase is that more relatively petty offenders are being sent to prison and sentences are getting longer.
The big failure in these circumstances is that "punishment" and "rehabilitation", the two competing justifications for imprisonment, have become irrelevances.
More failures include the number of people sent to prison who have serious mental health problems. According to the Home Office, 72% of male and 70% of female sentenced prisoners suffer from two or more mental health disorders and 20% of all prisoners have four of the five major mental health disorders.
The number of women in prison has more than doubled during the life of Tony Blair's government. Two-thirds of them have dependent children under the age of 18, and most under the age of 10. It is estimated that 150,000 children have a parent in prison.
And the number of children in prison and "secure training centres" has almost doubled in the last 10 years. Every year an estimated 70,000 school-age children enter the youth justice system.
Lastly, the failure to stem the number of suicides in prison. Since 1997, 790 people have taken their own lives while in penal custody. Adam Rickwood, at just 14, became the youngest prisoner in recent memory to die by his own hand in 2004 after being restrained by several members of staff and subjected to a measure to control difficult children in custody officially termed "nose distraction".
People often misquote Winston Churchill as having said that we can judge the level of civilisation in a society by the way it treats its prisoners. In fact, it was Fyodor Dostoyevsky who said: "The degree of civilisation in a society is revealed by entering its prisons." Winston Churchill actually said that a society's attitude to its prisoners, its "criminals", is the measure of "the stored up strength of a nation".
Churchill was home secretary when he made that speech, and just 35 years old, but clearly a world-class statesman and prime minister in the making. If we are ever to have a prison system of which we might be proud, instead of one that is a constant source of shame, Mr Brown, our new prime minister, would do well to take note of Mr Churchill's words or, like his predecessor, he will fail us.