I had arrived late at Mansfield's grand red-brick courtrooms, their façade dominated by a coat of arms and the Union Jack. Cherryl Lacey's court was already well into the day's business as I walked into a high, light and spacious room, expensively appointed in hardwood and glass. I'm glad we bother with the physical backdrop to our legal process: the calm authority that good design can convey. It matters.

But I tried to put such commentary aside. I wanted to see a day's work as Mrs Lacey and her two assistant lay magistrates would be seeing it. Magistrates hear and conclude (without juries) the overwhelming majority of criminal proceedings in England and Wales: all except the really serious crimes. I sat quietly until evening, watching - and trying to imagine myself in Mrs Lacey's place.

Trimly but unshowily dressed in a jacket and vest, bespectacled and flanked by two older white men, Mrs Lacey, a married mother of two, looked younger than her 54 years. Before her sat prosecuting and defence counsel. Behind them was a bench of seven defendants, some casually dressed, others looking awkward in Sunday suits. All had been arrested after a drunken Saturday-night fight outside Romans night club. All had pleaded guilty. Now they awaited sentence.

Mrs Lacey was listening intently as a defence lawyer entered a plea in mitigation for his client, who it seemed had initially failed to recall his involvement in the fight. But (said counsel) a police officer's mention of CCTV footage had jogged his memory. “I hit a guy 'cos he hit my mates.” I watched the CCTV evidence later with Mrs Lacey, and couldn't make head or tail of it. She could. She watches a lot of this.

The defendant's plea in mitigation, eloquently made, was the usual stuff: difficulties at home; no contact with his father; recently watched his grandmother die in agony; good character; “devastated” by his folly; working as a roofer; desperate not to go to prison and lose his job.

“Don't you worry you might be taken in,” I asked Mrs Lacey at the end of the day, “by sob stories?” “Not really. Some are true, some you can't be sure. That's why it's important we come from the communities where we preside; we do get a sense of things. Anyway, you have to keep thinking about the offence.” Later I watched her cock her head as a defence lawyer suggested his client's conviction would be punishment enough, as it would horrify his girlfriend when she found out. “But didn't you say earlier she answered the door when the police called?”

Everyone called Mrs Lacey “Marm”. The whole court stood when she and her fellow-magistrates entered or left. “It took some getting used to,” she told me later.

Her regular job is in an infants' school. She's a teaching assistant. It takes a bit of juggling to fit her morning, afternoon, or sometimes all-day court sessions, alongside work and home; but she and the other lay magistrates do manage to combine their court work with responsibilities in very different walks of life.

That day it seemed all human life in Mansfield was paraded before Mrs Lacey's court. A girlfriend wept uncontrollably in the visitors' gallery behind a glass screen, her hands shaking as her boyfriend (part of the Romans Club affray) quailed before the Bench.

“Does it influence you,” I later asked Mrs Lacey, “if there are relatives weeping in court?” “Sometimes it's useful to know if a convicted person is going to get any support,” she said, deftly.

A pale, thin, anxious youth, barely 17 (no previous convictions) clenched and unclenched his hands as he tried to explain missing a court appointment, after his futile theft of a motor scooter. He was living at home and due to start a job on the minimum wage, “valeting cars” (he stammered). “He gets his dates mixed up,” his lawyer said. Didn't this daily parade of inadequacy and hopelessness depress Mrs Lacey? No, she said: returning to control unruly tots helped her hold on to her bearings.

Then a sign of our times. A woman in her late thirties, thin-faced, sharply dressed, tense, was applying to have her three-year driving ban (she'd drunk too much after splitting with a partner) lifted after two years. The estate agency where she worked had valued her so highly they'd kept her in a desk job, but now with the property market flat they couldn't carry an employee with no car. And if she lost her job then her house (she had a 100 per cent mortgage) would go, too.

Her relief when the Bench granted her plea was palpable.

Few of those before Mrs Lacey's court were seriously wicked. They were just making the most awful mess of their lives. Often tears pricked my eyes. And hers? Did a soft heart beat beneath that businesslike jacket? Over a simple lunch of sandwiches (“big lunches are out; you have to really concentrate”) she replied that she never forgot the purpose of law; and never forgot the victims. I found her not cold-hearted but hard-headed. Dealing with schoolchildren, she said, wised you up.

It had also given her a sort of command. “Hands out of your pockets,” she had said firmly to some wretched youth standing before her - and he had blushed and complied. I think I saw his mother wince.

I watched as Lacey and her colleagues retired to confer before passing sentence on the seven youths. Crestfallen and scared, most had not been in trouble before. One who had risked prison.

After long deliberation (“a lot of it is behind the scenes, conferring,” she had told me) the Bench filed back. All the youths got more than a hundred hours' community service, and one a suspended prison sentence, too. Before sentencing, Mrs Lacey gave them a headteacher-like lecture - quiet, steady, severe - on the serious nature of their offences. They left her court looking shaken.

And I thought as I left of all the tens of thousands of Cherryl Laceys and their male counterparts quietly dispensing justice. A good mind, decisive judgment, a spirit of public service, and a commonsense understanding of what makes people tick were their qualifications.

I didn't recognise in Cherryl Lacey's Mansfield court The Daily Telegraph view of a Britain of over-indulgent justices and soft punishments. All these lads had done was get into a fight outdoors. With each other.

Outside, I chatted with a local about it, and the men Lacey had sentenced. “Youths is alus fightin',” he said, “nowt you can do about it.” Let him try saying that in Mrs Lacey's court.

Next week: Libby Purves dons her stab-proof vest

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