The case of Craig Sweeney first brought the debate into the public domain.

Sweeney, 24, kidnapped a girl, aged 3, from her home in Cardiff in January 2006 before attacking her. This month he was jailed for life and told he should not be considered for parole for at least five years. The victim's family attacked the sentence for being too lenient. In turn, John Reid, the Home Secretary, said he would be writing to the Attorney General to ask him to consider referring the sentence to the Court of Appeal as "unduly lenient".

How do judges calculate prison sentences?

Anyone convicted of a very serious offence, such as murder, rape, or violent child abuse, will normally receive an indeterminate or "life sentence", where the judge has a discretion to impose the minimum time the offender must spend in prison. This minimum sentence is called the tariff, and it is also the period the defendant must spend in prison before a prisoner can be considered for parole.

To calculate the tariff, the judge will take into account any discount for a guilty plea, usually a third if the defendant pleads guilty at the earliest opportunity. The judge will also take account of the possibility that a model prisoner will be eligible for parole after serving half their sentence. To ensure that sentencing is consistent across the country, the Court of Appeal used to set guidelines for judges to follow. But this role is now performed by the Sentencing Guidelines Council, an independent body set up by the Government. Its membership includes the Lord Chief Justice, who heads the judiciary, and the Director of Public Prosecutions, who is in charge of the Crown Prosecution Service.

Are criminals receiving more lenient sentences?

According to the most recent figures, complied by the Prison Reform Trust, offenders are being sentenced to harsher prison terms than they were more than 10 years ago. The average length of a custodial sentence in the crown court has risen from 20 months in 1993 to 27 months in 2004. The use of prison in magistrates' courts has risen from 6 per cent in 1993 to 16 per cent in 2004. There is also a much greater tendency to send petty offenders to prison.

Two years ago, 9 per cent of shoplifters with no previous convictions were sent to prison from magistrates' court, compared with 2 per cent in 1993. The number of life sentences has more than doubled in a similar period, from 3,000 in 1992 to 6,431 last year. The reason, according to a South Bank University study based on interviews with 122 judges, was that sentencers responded to the political climate.

So why are politicians accusing judges of being too soft?

Many observers of the criminal justice system are of the view that the Government, led by the new Home Secretary, John Reid, has chosen to pick a fight with judges because it will boost Labour's sagging ratings in the polls. Criticising judges for not being hard enough on criminals strikes a chord with some sections of the electorate. It is also significant that government attacks have coincided with a newspaper naming and shaming campaign featuring judges who resist imposing maximum sentences.

Is the Government unified on this?

In a word, no. The Attorney General, Lord Goldsmith, has made it known that he was unhappy that a member of the Government publicly referred the Sweeney case for his attention. Lord Goldsmith is supposed to be independent of Cabinet when deciding which "unduly lenient" cases are suitable for referral to the Court of Appeal. Mr Reid's intervention may have prejudiced any possible appeal. Last week the Lord Chancellor, Lord Falconer, entered the row when he defended the role of judges on BBC1's Question Time. But on Saturday one of Lord Falconer's junior ministers said she thought Judge John Griffith Williams had got the Sweeney sentence wrong. In contradiction of Lord Falconer, Vera Baird QC told BBC4's Any Questions that she thought the judge had made three errors in his calculation of the tariff. Following "discussions" over the weekend with Lord Falconer, Ms Baird was forced to make a public and very humiliating apology for her remarks.

Haven't we been here before?

From time to time Home Secretaries have attacked judges when the political climate was right. Michael Howard, when he was responsible for law and order, caused a huge row when he took issue with the then Lord Chief Justice over sentencing tariffs. Lord Woolf, when he was Lord Chief Justice, was criticised in 2002 when he issued guidelines which some newspapers said would encourage judges to give burglars non-custodial sentences. More recently, David Blunkett found it hard not to express his personal disdain when court rulings went against him. But the current sour relations between the judiciary and the executive is the most serious yet.

Why don't the judges stand up for themselves?

There is a constitutional convention that sitting judges do not express opinions on subjects that they might have to rule on. Because of their unique place in our democracy, they must be seen to be impartial. Under the new constitutional reforms the Lord Chancellor now has a statutory responsibility to defend the independence of the judiciary so that individual judges don't feel the need to speak out. Even so, in the past week some judges have felt compelled to make public statements, pointing out that the calculation of a prison sentence largely depended on criminal justice legislation that had been passed by Parliament.

How will it all end?

The Government says it will bring in yet more measures to help judges to set longer jail terms. Lord Falconer wants to look at ways of abolishing the rule that gives defendants an automatic discount on their sentences if they plead guilty. He says there will now be a full review of the statutory sentencing framework.

Are the judges being too lenient?

Yes...

• Some violent crime is increasing because offenders don't believe they will receive a long prison sentence.
• Re-offending rates have also increased suggesting judges are not imposing sentences harsh enough to deter criminals.
• Judges live in different world and are out of touch with popular desire for even tougher sentences than they are passing

No...

• The government's own figures show that the average custodial sentence have increased since 1993.
• Sentencing policy is the responsibility of the government not the judges.
• Judges follow strict guidance set by the new Sentencing Guidelines Council introduced under Labour.