More than 600 judges have condemned government plans for new sentencing guidelines as “unnecessary, costly and unwelcome” and likely to lead to injustice.

In a strong and highly unusual intervention, the body that represents the 652 circuit judges in England and Wales has warned that changes going through Parliament will severely limit judicial discretion.

The Council of Circuit Judges says that the Coroners and Justice Bill will introduce “mandatory guidelines which the court must follow or apply in reaching the sentencing decision”. It said: “We do not consider these sentencing proposals to have any benefit. The proposals are not sought by the judiciary or any other criminal justice group. They are unnecessary, costly and unwelcome.”

The Bill has passed through the Commons but has yet to go through the Lords, where the judges are likely to receive substantial support. They believe that the proposals will lock them into a rigid framework of sentencing options.

The Bill also seeks to remove the discretion of the Sentencing Guidelines Council “by requiring it to structure guidelines in a rigid way”, the judges add. “The discretion of the sentencing judge is thereby severely limited by the introduction of what are mandatory guidelines which the court must follow or apply in reaching the sentencing decision.”

The judges accuse the Government of departing from recommendations made by a working group set up under Lord Justice Gage in 2007 to consider an American-style sentencing grid. Its report called the idea “unsuitable and unacceptable in England and Wales”.

Jack Straw, the Justice Secretary, sought to defuse the issue last night, insisting that he was not introducing mandatory sentencing guidelines. “I share the objections of the Council of Circuit Judges to what they describe as mandatory guidelines,” he said. “But this is not what is contained within the Bill.”

He said that on Tuesday he had moved a series of amendments “to underpin judicial discretion, and to ensure greater necessary flexibility for the sentencing court” that MPs agreed. The Bill also spelt out that the sentencing court could depart from the already flexible guidelines “where it is in the interests of justice to do so”. Mr Straw said that he was willing to meet judges to discuss concerns.

A spokesman for the Ministry of Justice said that the Bill intended to ensure “greater consistency in sentencing, which would be in the interests of justice and, primarily, of the public”.

Similar concerns have been expressed by the 30,000-strong Magistrates’ Association. Its chairman, John Thornhill, said that magistrates were “angry and upset over what they see as an unwarranted attack on their independence”.

The association said yesterday it understood that it was not the Government’s intention to remove judges’ discretion or to tie sentencing decisions to the availability of prison places. It added, however, that “amendments proposed are not strong enough to allay fears that undue influence through a too rigid sentencing structure will be imposed”.

Keith Cutler, of the Council of Circuit Judges, said: “Sentencing is an art, not a science. We believe the current system is working and that there is no need for any new structure.”

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