Last Night's Viewing: The Strange Case of the Law, BBC4 Silk, BBC1

Dear lord, he must be sick of the jokes by now. Harry Potter, I mean, who I assume led a pretty untroubled existence for the first 40-odd years of his life, initially as a prison chaplain and later as a defence barrister.

He was called to the bar in 1993 and then, four years after that – five if you allow a bit of time for the craze to build – he suddenly found himself in a world where no encounter would be complete without a lame crack about wands or wizardry.

Judges, who know a captive audience when they see one and have little compunction about using it to build their reputation for judicial wit, probably never leave the poor chap alone. A lesser person might have changed his name by deed poll, but here he is – presenting a BBC4 series on English law – and he barely flinches when he introduces himself.

He doesn't mess around with mimsy qualifications either. "The story of England's law is nothing less than the story of England's people," he declared robustly at the beginning of The Strange Case of the Law. More than that, it exceeds anything we've achieved in the arts and sciences, in his view, and constitutes our greatest gift to the world (eat your heart out, Shakespeare, Newton and Darwin). And the key to that gift, in Potter's view, is the willingness to put lay people at the heart of the system, in the form of a jury.

The story he tells, considerably simplified, is one of the nationalisation of redress. He began in Rochester, with the Textus Roffensis, a collection of laws from the reign of Aethelbert onwards. At this point, justice appeared to consist simply of a tariff of reparations for injuries sustained, to be enforced (after due negotiation) by the plaintiff's relatives. A little later the King took the large step of making himself – or the Crown – an effective co-plaintiff in every case, since it was his peace that had been breached. And from there the state increasingly administered, systematised and enforced the law.

It was also a story of a journey from superstition to adversarial argument. Very early justice was based on oath-giving and character witnesses, the idea being that the consequences of lying to God were so terrible that nobody would take the chance. After that the notion of the ordeal was introduced to trials, with accused parties being required to walk a few paces carrying a piece of red-hot iron.

There was no question that everyone would get horribly burned, but only the wounds of the guilty, it was argued, would start to suppurate. When William the Conqueror arrived, he added trial by combat, which meant that the thug who'd beaten you to pulp got the opportunity to do it again to prove he hadn't. And then, thank goodness, we were on our way to habeas corpus and m'learned friend and all that.

Potter's manner in presenting this material is rather chewily forensic. He addresses the camera as if he suspects that it might witholding an important piece of material evidence. And there's a matching pugnacity to his arguments that can be rather bracing. You might think that Thomas à Becket is a sainted martyr who died in the cause of conscience.

Potter thinks of him as an obstructive reactionary protecting an indefensible privilege – the right of the clergy to exempt themselves from the reach of the common law. "The clerical child-abuse scandals of recent years are Becket's legacy," he said sternly, as if wrapping up a closing speech to a jury. I rather liked that. I think he deserves his name back now.

If you think trial by combat is history you just need to watch Silk, the current series of which concluded last night in an absolute welter of professional misconduct and personal revelation. It makes less sense with every passing week, but the combatants are top notch.

Twitter: @tds153