A government minister who criticised a judge was under pressure last night to withdraw remarks that have threatened a fresh crisis of confidence between the judiciary and Labour.

Judge Keith Cutler suggested that comments made by Vera Baird, QC, a junior minister at the Department for Constitutional Affairs, called into question her future as a minister and could force judges to break their tradition of silence when criticised.

Mrs Baird, who was appointed to her first government post last month, reopened the row over "lenient" sentences by accusing Judge Griffith Williams, the Recorder of Cardiff, of getting the law wrong when he sentenced Craig Sweeney for kidnapping and sexual assault last week.

"The way he halved the sentence from 12 to six years is wrong," the minister said, referring to the minimum period of his life sentence that Sweeney would have to serve before being considered for parole.

Mrs Baird told Any Questions on BBC Radio 4: "I'm critical of the judge for three reasons: starting too low; deducting too much for the guilty plea; and getting the formula wrong."

These comments contradicted remarks made by her boss, Lord Falconer, the Lord Chancellor, two days earlier. He said it was not the judge who was at fault but the system under which he was required to operate.

If Mrs Baird does not want her ministerial career to become one of the shortest on record, she will have to promise Lord Falconer today that she will be more careful about her remarks in future.

Jack Straw, the Leader of the Commons and a former home secretary, yesterday sought to mend fences with the judges.

He told BBC1's Sunday AM programme that while some individual judges were open to criticism, prison sentences were going up and those for rape had doubled. He said British judges were "incorruptible, their reputation for fairness and the law is world class".

Lord Falconer told a private meeting of the Council of Circuit Judges on Friday that the sentence passed by Judge Griffith Williams was "perfectly proper and legitimate" within the provisions of the Criminal Justice Act 2003.

This was because the judge would have sentenced Sweeney to 18 years if he had been free to do so, a sentence that other judges regard as in line with the seriousness of his offences.

Lord Falconer's remarks went some way to reassure the judges after four days of press criticism last week, during which he had kept a low profile.

John Reid, the Home Secretary, appeared to support a campaign by the Sun newspaper against supposedly soft sentences by publicly asking his ministerial colleague, the Attorney General, to refer Sweeney's tariff to the Court of Appeal as "unduly lenient".

But Judge Cutler said yesterday that circuit judges had been "much heartened" by the Lord Chancellor's support on Friday.

"Before then, we were generally dispirited by what had happened during the week, and we needed to have some reassurance that he, as Lord Chancellor, supported the judges and was going to do all he could to look after our position."

He told Broadcasting House on Radio 4 that he preferred the Lord Chancellor's view of the law to Mrs Baird's. And he said some of his colleagues had felt that there was no one speaking on their behalf and might in future demand the right to answer back.

"We are thinking that we must perhaps change that, and that the tradition whereby a serving judge should not speak to the press is something which perhaps should be reviewed, because what otherwise happens is you have retired judges being asked to give comments on things that perhaps they're not quite up to date on.

"It's much better for a serving judge to be able to give a view - obviously not being able to comment on the individual case itself."