Plans to abolish juries in complex fraud trials do not amount to a general attack on jury trial, the Attorney General insisted yesterday.

Lord Goldsmith QC unveiled plans to enact a change in the law which was passed by Parliament more than 18 months ago.

It will allow a single judge to sit on complex fraud trials, forsaking the 800-year-old tradition that defendants are tried by a panel of 12 jurors.

The Government will move to introduce the law change in the autumn by seeking a vote in both the Commons and the Lords.

"This provision is not part of a general assault on jury trial," said Lord Goldsmith.

" The Government is strongly in favour of trial by jury in the vast majority of cases, where it will remain absolutely appropriate."

Civil liberties campaigners argued that removing juries from fraud trials was the thin end of the wedge which would lead to more types of crime being tried without jurors.

But Lord Goldsmith said: "If this were the thin end of the wedge it's the thinnest end of the wedge there can conceivably be."

The move was likely to involve between 15 and 20 cases a year, he added.

He said there was currently a "double standard" where convictions are gained in simple, petty frauds but more complex cases either have to be abandoned or never get before a court.

"We can't have a situation of easy-to-prosecute blue-collar crime and unprosecutable white-collar crime," he said.

"It is important that people running fraud at a much higher level should be brought to justice as well."

Former Law Lord Lord Ackner said: "I think there should be a presumption against trial by judge alone if the case can be dealt with within three months.

" The presumption still remains strong that trial by jury is fairer to the defendant than trial by judge alone."

Lord Goldsmith said it was currently too expensive, too difficult and too lengthy to bring some complex fraud cases.

"The Government believes that the answer is trial without a jury," he said.

The proposal would shorten trials, reduce costs and allow the full charges to be put before a court, rather than forcing prosecutors to water down allegations to make them manageable for jurors.

One recent high-profile case which may have been affected by the changes was the Jubilee Line extension fraud case, which collapsed in March after two years at a cost to the taxpayer of £60 million.

The Attorney General also produced a list of five other cases, one costing nearly £2 million, which may have been considered suitable for no-jury trial.

The right to trial by jury can be traced back to the Magna Carta in 1215.

The Government has already brought in measures which ended another ancient tradition - the double jeopardy rule - which said no-one could be tried twice for the same crime.

Director of civil rights group Liberty, Shami Chakrabarti, said: "This Government has long proved its lack of enthusiasm for our age-old traditions of jury trial.

"No-one should be under any illusion that this policy will stay restricted to serious fraud cases.

"Evidential complexity is an excuse that may be made with a whole host of trials."

She added: "This patronising approach is particularly surprising from a Government apparently so keen for greater community involvement in the criminal justice system."

Under Part 7 of the Criminal Justice Act - which gained Royal Assent in November 2003 - prosecutors will be able to apply to a Crown Court judge to allow the case to be heard without a jury.

The judge will be able to allow the application if "the complexity of the trial or the length of the trial (or both) is likely to make the trial so burdensome to the members of a jury hearing the trial that the interests of justice require that serious consideration should be given to the question of whether the trial should be conducted without a jury".

If a defendant is convicted by a judge sitting without a jury, the judge must give a judgment stating his or her reasons at the time of the conviction, or soon after.

Law Society president Edward Nally said the Government was wrong to act before the new court rules, introduced in March, took effect.

"Juries are not the reason for lengthy trials," he said.

"The solution lies in better case management and the new court procedure rules introduced recently must be given a chance to work.

"Without prejudicing justice, the new rules will ensure better management of cases and shorter trials."