The delicate task of keeping a jury on the road in a long-running trial requires a mix of firmness, diplomacy and hand-holding from judges.

The spectre hanging over all long trials is that of the Jubilee Line case, which collapsed with no verdict in 2005 after nearly two years. An inquiry found that it had placed an “intolerable burden” on jurors, disrupting their lives and blighting their job prospects. But juror sickness and time off also played its part.

The challenge for Mr Justice Calvert-Smith, a former Director of Public Prosecutions, was to keep the bottle bombers' jury going without losing numbers. As it was, the five-month trial was plagued by delays, illness and technical problems. The jury deliberated for a total of 52 hours, or 11 days — but spread over more than five weeks. One key reason was the holiday: two weeks for a summer break.

Maybe Mr Justice Calvert- Smith could have been stricter in managing the trial, but lawyers point out that he faced a difficult balance. John Cooper, a criminal barrister, said: “He would have had to have set a holiday period at the start of the trial [April] because he couldn't have been sure it would have been completed before the summer vacation.”

Every defendant has a fundamental right to a verdict determined by 12 people, so the judge has to balance the importance of a full complement of jurors coming to a verdict against the risk of losing jurors, and the verdict being delivered by fewer than 12 people.

Jurors are also becoming more assertive. One juror was not pleased when the judge stepped in, over his head, to try to move a medical appointment — so that time would be saved. The foreman sent a note saying that they were exhausted and upset by the “cavalier attitude” of the court to their wellbeing — and demanded a day off. The judge had no option but to agree. “There is a view that they were getting a bit too big for their boots,” one observer remarked.

The judge also allowed a three-day break because one juror had a training course. Then another's granddaughter was taken seriously ill. Mr Justice Calvert-Smith tried to move things along by extending sitting hours, but jurors became troubled by stomach upsets and migraines. One injured his foot and took time off for two hospital appointments.

The Jubilee Line inquiry found that jurors were not always treated well and that judges and court staff had to remember that they are a key part of a trial. But jurors must ensure that they do not fuel the opinion that, in long trials at least, their time is up.

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