The unprecedented trial of four alleged armed robbers without a jury has begun as a barrister for one of the men said: "We are breaking history."

John Twomey, Peter Blake, Barry Hibberd and Glen Cameron are accused of taking part in a "professionally executed" £1.75 million hold-up at a Heathrow warehouse in February 2004.

The Court of Appeal ruled last year that the case should be heard by a judge alone because of the danger of jury tampering.

It is the first major criminal trial in England and Wales to be held without a jury, and is taking place at the Royal Courts of Justice.

As the case was about to open it was the judge, Mr Justice Treacy, who was formally put in charge of the defendants by the clerk of the court, rather than any jury.

Earlier during legal submissions Sam Stein QC, for Hibberd, remarked: "We are breaking history. This is the first time that a court has started a jury-less trial."

Twomey, 61, of New Milton, Hants; Blake, 57, of Notting Hill, west London; Hibberd, 43, of Shepherd's Bush, west London; and Cameron, 50, of New Milton, Hampshire all deny a series of charges including robbery and firearm possession.

As prosecution barrister Simon Russell Flint QC was about to open the case, the judge explained how he had decided to adapt the normal procedure by which juries are given responsibility for a case.

He said: "At this stage the defendants would have been put in the charge of the jury and, although it is not apparently a strict legal requirement that they are, I have asked the court clerk to adapt the normal formula and to put me in charge of the various counts on the indictment."

Then, instead of reading out all 18 charges as she would have done to the jury, the clerk simply asked the judge to confirm he had seen the indictment. She then informed the judge that the defendants had pleaded not guilty and that it was in his charge to say whether they were guilty or not - the task usually given to jurors.