There’s a whole category of threats, insults and exhortations that angry people shout without literally meaning what they say. “Go to hell” is an obvious example. (Pragmatically speaking, how would that help to resolve a dispute?) That uncouth American riposte “kiss my ass” is another. I mean, really? Wouldn’t you rather have your rump pecked by someone you actually liked?

And a third is “I’m going to sue under the Trade Descriptions Act”. In the 41 years since that piece of legislation came into effect, the phrase must have been uttered millions of times. The world is full of package holidays, lap-dancing clubs, hair restoratives, politicians, second-hand car dealers, dream apartments, religions, train companies and self-improvement manuals that deliver nothing like what their advertising promised. Livid at being duped, many of us must have shouted those words at least once in our lives. But who has the time or knowhow to carry through the threat? I’ve met some furious ripped-off punters in my time, but I’ve never come across any who did sue under the Trade Descriptions Act, let alone win.

Until now.

Last week, Manchester County Court was the scene of an extraordinary victory. A man called Adrian Bradbury had taken his family to see a professional staging of The Wizard of Oz at the Lowry Theatre in Salford. I know the Lowry well. It’s a superb arts centre and it usually puts on top-class shows. But The Wizard didn’t enchant Mr Bradbury for one simple reason. It had no live band.

All the songs and dance routines were performed to pre-recorded backing tracks. Mr Bradbury felt that if you had paid to see what was billed as a “magical family musical” you were entitled to expect live musicians. So he sued under the Trade Descriptions Act. And, astonishingly, he won. The Lowry argued that “133,000 theatregoers have enjoyed The Wizard of Oz at the Lowry and Mr Bradbury was the only person who expressed any concern with the lack of live music”. But the judge, in effect, said “so what?”. He ruled that Mr Bradbury’s personal expectation of hearing real musicians was genuine and reasonable. So the Lowry must now refund the £134.50 that he spent on tickets.

You may sense that there’s a lot of subtext nestling behind this apparently simple tale, and you’d be right. Mr Bradbury is no ordinary punter. His dad, Colin Bradbury, was principal clarinettist of the BBC Symphony Orchestra for 30 years. His brother (who also saw the ill-fated Wizard) is also a professional clarinettist. He himself is a distinguished cellist. His case has the enthusiastic backing of the Incorporated Society of Musicians. And in court he produced an expert statement from none other than Sir Harrison Birtwistle. Britain’s leading avant-garde composer isn’t known as a connoisseur of kitsch Broadway musicals, but he nevertheless declared helpfully that without an orchestra or musical director “a performance of The Wizard of Oz is best described as karaoke”.

You get the picture. This is more than a bee in one man’s bonnet. It’s a backlash by an entire profession. For years jobbing musicians have fumed as backing tracks replaced them in more and more ballets, musicals, cabarets and talent contests. The Lowry’s Wizard is one of hundreds of band-less shows round the country. Now, finally, they see a way of stopping the rot.

If it were simply a matter of protecting their own jobs, they wouldn’t have much of a case. After all, advances in computer technology have devastated thousands of occupations, from telephonists and filing clerks to printworkers. Musicians deserve no special immunity.

But the issue is really an ethical and aesthetic one. Why do punters pay to see live entertainment, as opposed to sitting at home and watching the telly or playing a DVD? The answer is that they want to see a performance created afresh before their eyes, not synthetically recycled with minimum effort. A performance that can vary subtly, or a great deal, from night to night. One that responds to the changing mood of the audience or the performers. One that exhibits high theatrical and musical skills. One that requires superb teamwork if all its elements are to be kept in perfect alignment. One that might go wrong, unless everyone gives 100 per cent.

Backing tracks remove a large measure of that danger, as well as any display of instrumental skills. But they also bind singers and dancers to the same speeds, the same interpretations, the same phrasing, for show after show. That vital musical ingredient called “rubato” — the flexibility to slow or quicken the pace on the spur of the moment — is eliminated.

In effect, the audience is being hoodwinked. They are paying to hear live music — yet spontaneity, the very essence of live performance, is ruled out.

A county court judgment doesn’t set a binding legal precedent, so Bradbury v Lowry can’t yet be called a landmark ruling. Nevertheless, it opens up all sorts of possibilities. Will Simon Cowell, for instance, be shamed into using a live band for the rounds and finals of Britain’s Got Talent? It’s not as if he doesn’t have the spare change. And shouldn’t a show that makes such great play about discovering unknowns who can perform brilliantly live on stage be using real musicians to back them, rather than (as Birtwistle would see it) a glorified karaoke machine?

And what about the vexed question of miming? Is it strictly legal for Britney Spears, Madonna and other luminaries to pass themselves off as live singers when so many numbers in their stage shows are lip-synched to pre-recorded tracks (and usually lip-synched rather badly, too)? Granted, most of their fans don’t seem to care. They’ve paid to see the spectacle, or soak up the atmosphere, or bask in the star’s charisma. But what a deliciously humbling lesson it would be for these multimillionaire chanteuses if they were forced to print the words “she’s miming, you know” on all the tickets for their supposedly live shows.

Belatedly (since it is now being replaced by new European legislation) I’m starting to warm to the Trade Descriptions Act. Mind you, when applied to musical matters it’s a dangerously blunt instrument (as it were). Is it even possible, I wonder, that Harry Birtwistle himself could be sued by an uncomprehending listener for passing off what he writes as music? Now that would be a fascinating test of semantics, artistic taste and the laws of the land.

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