Twelve confused men and women

"Madam foreman, on the first count do you find the defendant guilty or not guilty?" the court clerk said.

My throat went dry and for a moment my voice failed to work. "Not guilty," I forced out. The defendant's friends broke into cheers, the judge yelled, "Shut up!" and all I could think of was "what have I done?" This was my the culmination of my experience of the parallel universe known as jury service, where I had been summoned to spend 10 days closeted most of the time from the outside world, confined almost as much as the defendant.

Robert Frost, the American poet, once described a jury as "12 persons chosen to decide who has the better lawyer". Juries have been in existence since the 12th century to decide the facts in a case proved by the evidence presented in court, and to judge their peers. Which was fine in the 12th century, when legal processes tended to be fairly informal. But after spending two weeks in a London courtroom, I began to feel that ignorance of the law and increasingly complexity of cases are making it more and more difficult for juries to reach a true verdict according to the evidence, as they swear to do.

Not that such thoughts strike you upon stepping into the court building on a Monday morning. First, you are hustled along corridors like rats in an elegant Victorian sewer, until you reach the jury lounge and canteen. You turn up in a suit on the first day to impress the judge and live the rest of the time in jeans. You hope to avoid the local mafiosi trial after being confronted with scary posters along the walls saying, "How many lives have you got? Be vigilant."

You are kept for hours in the jury canteen sipping endless cups of coffee and reading John Grisham novels (on my first day I counted around 10 people reading The Client, The Firm or The Rainmaker). If you didn't bring a book then the hours are whiled away by one of the games kindly left by the jury bailiffs, such as one called Snap Judgment, which involves trying to solve cases. Significantly, someone had removed the instruction booklet.

Called finally, there is no detailed interrogation of your prejudices or your suitability to sit on a jury. There are no OJ-style challenges. Instead, a jury bailiff shuffles a set of cards with names on and picks out the lucky ones. The rest are left disconsolate, like those chosen last for school netball. Even then, 15 people were sent to each room in case any of the jurors were challenged. No one I met ever was.

The two weeks I served on a jury I had to deal with a date rape case and one of ABH (actual bodily harm), where a man had allegedly scalded his girlfriend's four-year-old son. (These rated well in the canteen pecking order: DSS fraud was generally considered the worst case to get).

Sworn in on the first case - the rape - for the first 10 minutes, I enjoyed sitting in the jury box instead of the Press benches. It was a relief not to worry about what the story would be. I imagined myself as part of Kavanagh QC or Rumpole of the Bailey listening to the opening speeches as if trying to unravel a logic puzzle. Then, as my eyes veered to the left, it struck me with a sudden force. I had the power to send that man in the dock to prison for a very long time. It was two lives I was dealing with here, not a 300-word story. The defence's continued objections were no longer a nice legal device but something used deliberately to sway my opinion.

I had considered myself fairly well-acquainted with the law - after all, I've reported on enough court cases. But led to the retiring room by the jury bailiff, I realised that I knew nothing at all. Take that most innocuous of phrases, "Beyond reasonable doubt". The prosecution had urged common sense, the defence the gaps in the evidence. But they both insisted, as did the judge, that we had to be sure before returning a guilty verdict.

But one person may only be convinced beyond reasonable doubt if there are three eye-witnesses and hard photographic evidence, proving that Professor Plum was in the conservatory with the candlestick. For others, the fact that the defendant was unable to look them in the eye or paused before answering a question could be indicative of underlying guilt.

The image of jurors is that of avenging angels eager to send anyone down, while picking up their pounds 44.80 daily allowance. But most jurors take their duty seriously and prove reluctant to convict unless they feel irrefutable evidence has been given to them.

Medical evidence is even more fraught with difficulties. I thought that there were several red herrings in the different explanations of how the child's injuries had been caused. But I'm no medic, and how could I prove this beyond reasonable doubt, to myself or my fellow jurors? It is no longer enough to say: "Have you forgotten Magna Carta? Did she die in vain?" for your 11 co-jurors to be persuaded to your viewpoint. And I was amazed at the prejudice that I encountered, particularly in the rape case where there were only three women on the jury. Following last week's shenanigans, when a barrister can imply that a woman's choice of dress leaves her vulnerable to being stalked, maybe this should be no surprise. But I was still annoyed to be told after the case had finished that women going out to nightclubs were obviously going out to "get laid."

Jury service left me with two strong convictions. One is that everyone should do it - the experience of holding someone's future in your hands is frightening, but it challenges your world view. You learn to listen to other people and not dismiss them out of hand, however tempting it is initially (and believe me, I was tempted.)

But while everyone should do jury service, I don't believe it works, or not in the form we have at the moment. Unless we start giving jurors a crash course in the law, or at least some clues as to what previous good character and reasonable doubt actually mean legally, the justice system is better off with just a judge. The juries I sat on were working in the dark at the mercy of clever barristers who did little to make the law clearer. There was little conclusive evidence in either of the cases that I covered, and I was at a loss to cope with the complex issues in the law, as I think were most people.

"Consider what you think justice requires and decide accordingly," said the Earl of Mansfield. "But never give your reasons, for your judgment will probably be right, but your reasons will certainly be wrong." I have no doubt that we returned the right verdicts. But the reasons behind them?