The number of people being given life sentences has more than doubled in the past 10 years while judges have been imposing longer prison terms each year.

The Sentencing Guidelines Council counters the Prime Minister's claim that Britain's courts are not being tough enough on convicted criminals.

Its research, published yesterday, shows that judges are imposing harsher prison sentences than ever before. At the same time overall crime levels are falling.

In 1993 the Crown Courts imposed 382 life sentences compared with 581 in 2004. The average prison sentence in the Crown Court increased by seven months in the same period. But Tony Blair insisted yesterday that more laws were needed to "rebalance" the criminal justice system. This week the Prime Minister also blamed the courts for the public's lack of confidence in sentencing.

The SGC, an independent body which gives guidance on sentencing, also found that the biggest increase was for burglary. The average sentence for stealing from a home has risen from 15.3 months to 24.9 months in the past 10 years.

It says: "Changes in both custody rates and sentence lengths have been reflected in the large increase in the sentenced prison population ... One month's change in the average sentence length changes the adult sentenced prison population by approximately 1,800."

The picture of a criminal justice system driven by a culture of custodial sentencing first emerged two years ago in an independent report that drew on interviews with 133 judges and magistrates. It showed that the political climate is having a greater impact on sentencing than the Government is willing to admit.

The South Bank University study undermines the view that the courts are too soft on criminals. It identifies two factors in the rise in the prison population - the jailing of offenders who would previously have received community penalties and the courts' willingness to impose longer sentences.

The report's author, Professor Mike Hough, the director of the university's criminal policy research unit, said many of the judges and magistrates interviewed said they would like to see tougher community sentences.

Mr Blair said more legislation was needed to address what he saw as shortcomings in the criminal justice system, which prompted allegations of "swamping" the courts with new laws.

The Commons library lists 60 Home Office Bills brought in since Labour's 1997 victory, partly won with the mantra "tough on crime, tough on the causes of crime". Not all were directly related to crime, but the majority, 34, had criminal justice at their core.