Not everyone knows it, but I've been a maestro for years. I have charged through Brahms's Third on the Metropolitan Line and swooned through Mahler's Fifth on the Circle Line; I have led an apocalyptically frenzied Verdi Requiem in the comfort of my own living room, fed by the kind of furious rage that probably would have resulted in physical harm had it not been for my wonderful leadership of the Vienna Philharmonic.

Of course, I haven't actually got as far as the baton, the concert tails or even the orchestra. That is, not unless you count those ever-so-responsive players in my head or on my iPod, the ones who always know exactly how I want to pace that diminuendo or finesse that accelerando. But now it has all become terrifyingly real. I have been given 15 minutes at the BBC's rehearsal studios for its latest reality show, Maestro, in which a motley crew of celebrities, including the actress Jane Asher, the DJ Goldie, comedienne Sue Perkins and former Blur bassist Alex James compete to become the best conductor in time for a public vote next month. The winner will get 15 minutes with the BBC Concert Orchestra at the Proms in the Park.

How hard it can it be? A 70-piece ensemble is waiting expectantly for my downbeat for the first movement of Beethoven's Fifth. What kind of a maestro should I be? The conductor is, after all, not the karaoke conduit I have been play-acting for years. He is mentor, scholar, motivator, interpreter, leader, follower, idol. He is all of those and none, a cryptic figurehead who can mean everything or nothing depending on what he brings to the performance.

And now he is a prize ass. I step up to the podium exuding what I think is a fatherly authority; I leave a chastened schoolboy, the kindly giggles of a viola player ringing in my ears (violas are the bullied pond scum of the orchestra, so this is doubly humiliating). My beat is feeble, my body language weaker yet. If the iconic opening bars of Beethoven's Fifth are supposed to depict “fate knocking at the gate”, then my paltry wrist action makes it sound as if the gate has just managed to punch fate in the face. Eventually it all falls apart completely: when I fall slightly behind, I make the elementary error of galloping ahead and manage to turn a smudgy mess into a sonic catastrophe.

Beethoven's Fifth crackles along with just one beat per bar. I did spend 15 minutes with the series consultant, Peter Stark, in which I was taught the rudimentary gestures and told how to adapt to match the time signature and rhythm. But it means setting a distinct, vigorous and regular pace from the start that doesn't flatten one of the most dramatically charged pieces in the history of classical music. I just haven't got the pulse of it at all.

What's the secret? Well, a conductor has only two jobs. The tricky thing is that the first - keeping time - takes weeks to learn, and the second - leadership - takes a lifetime.

“There is a mystique about conducting, whether you're a player or in the audience,” says Brad Cohen, the professional conductor who is mentoring Alex James throughout the BBC series, “and there's something intangible about it that's very difficult to explain. We can try to dissect it, but there is something that remains that no one really knows - and that's the magical aspect of conducting.”

Later on, unlike me, the celebs are not letting their technical handicaps (most of them can't even read music) get in the way. While Jane Asher is admittedly letting Mozart's overture to The Marriage of Figaro fall flatter than a collapsed soufflé (not one of hers, obviously), the orchestra seem able to see through any gaffes and connect to something deeper. They keep it together. “You have to exude a certain sense of authority and confidence that you're probably not feeling at all,” she confesses. “If I make a mistake I keep going and hope that nobody notices.” Which takes me to my next failing: I don't exude confidence at all. I look as if I'm waving a toothpick at a charging elephant.

Once it was simple: the cult of the conductor, which reached its height in the middle of the last century, led to the maestro soaring to an august position in the musical hierarchy. He received by far the biggest cheque, too, a string to his bow that the best-known conductors preserve (and a secret they guard closely). But when the notoriously demanding Lorin Maazel signed up as music director of the New York Philharmonic in 2000, there were rumours of a fee totalling about $2 million for only 14 weeks spent in the city each year.

But if Maestro has a point to make, it is that old-fashioned mystique and snooty manners just don't cut it any more. Forget the tyrants of old, the men with fearsome names such as von Bülow, Walter, Mravinsky, Weingartner, Koussevitsky, Busch, Beecham: the conductor of the 21st century cuts a more approachable figure. According to Cohen, “different kinds of orchestra need different kinds of leadership - the mistake is to get trapped in one style. There are many parallels between managing groups in rehearsal and managing people in a business organisation.”

Perhaps this explains the extinction of the big beasts: slow death through the language of human resources. How could a man such as Fritz Reiner ever get his hands on an orchestra now? The legendary boss of the Chicago Symphony Orchestra never even looked at a double bassist if he could avoid it, and certainly never bothered to have a conversation with one. “That would not be tolerated now on so many grounds,” says Cohen. “We should all lead and inspire in a way that creates respect.”

It is a feeling echoed by the other young conductors at Maestro. “It's important that conductors put the music first and not themselves,” says Jason Lai, who is mentoring Sue Perkins. “Often I go to concerts and I think 'Oh, that was a great performance of Beethoven', but I wasn't hearing Beethoven - I was hearing the conductor.” Maybe this is why the Perkins baton technique is more flowing, more empathetic than Asher's, and why Lai encourges her in rehearsal to “see how little you can get away with” when it comes to movement and motion.

To discover just how far the battle lines have shifted in the relationship between conductor and orchestra, you have only to talk to a player at the Orchestra of the Age of Enlightenment, which prides itself on its “corporatist” outlook to musicmaking. And whether their maestro is leading Bach or Brahms, the players are not interested unless they get their input, too. “The conductor is more like the first violin,” says the OAE violinist Nicholas Logie. “It's a far more democratic relationship, and in the OAE nobody is shy about saying anything in rehearsal.”

Ask Logie, Cohen or Lai who their idols are and they will mostly likely point you to the model of the modern major maestro, Sir Simon Rattle - “the figurehead to a different style of persuasion”, as Cohen puts it. And that would be fine, were it not that for every Rattle, who commands absolute respect from arguably the most demanding orchestra in the world (the Berlin Philharmonic), there is another touchy-feely conductor without Rattle's immense charisma - or his ability to get the world outside the concert hall to sit up and notice him.

“I don't believe that good music-making is democratic,” says Jonathan Freeman-Attwood, principal of the Royal Academy of Music. “It takes artistic leadership to make special things happen. If everyone is terribly pally then people don't play on the edge of their seats because they don't have a sense of a real presence there.” He is concerned that the newest generation of conductors are being pressurised simply to be adaptable above all else in a world where much of the money is to be made outside the concert hall, whether by recording film music or by leading musicals in the West End.

“The conductors who get work today are the ones who can do the shows on an afternoon and an evening,” says Freeman-Attwood. “Those may be the most flexible, the most charming and communicative ones, but they may not always be the musicians who have what it takes to say something really important and profound about Bruckner's Eighth Symphony.”

Well, none of the Maestro candidates will get a crack at Bruckner - not unless there is a drastic improvement first. They are, after all, mostly here simply to remind us how hard a job this really is. But watching them does tell me something about that all-too-elusive “presence” that Freeman-Attwood is after. Asher has it with an old-school glare. Perkins has it through empathetic bonding. Even Bradley Walsh (once upon a time Danny Baldwin in Coronation Street) yomps through a bawdy slice of Khachaturian with admirable joie de vivre.

Watching them, I realise that it wasn't just my feeble beat that sank the Beethoven: it was my performance. “Conductors are all big personalities,” says Cohen. “You have to have incredible reserves of self-belief and force to stand up week after week with varying orchestras with varying degrees of resistance. And the big personalities will not go away.”

Speaking from lily-livered experience, from now on this personality is sticking to the safety of the stalls.

Maestro starts tonight at 9pm on BBC Two

Lauded and loathed: what makes a real maestro

Conductors are the most powerful beasts in the classical music jungle, and also the most detested. The violinist Nigel Kennedy's outburst this year, when he called them overpaid, egotistical and mostly useless, produced approving nods in the orchestra pits where highly trained instrumentalists toil for a pittance under well-paid maestros who are sometimes far lesser musicians.

So in theory it may seem possible to teach a beginner enough tricks of the conducting trade for him or her to pass muster, at least temporarily, on the podium. In reality (as opposed to reality TV) it would be cruel and ludicrous. Orchestras play all sorts of pranks on new conductors to see if they are up to scratch, from inserting wrong notes or omitting correct ones to lagging wilfully behind the beat or charging in front. If the would-be maestro can't hear what is going on and put it right, he is doomed. I have seen rehearsals disintegrate into anarchy in such cases. It's like not standing up to the playground bullies on your first day at school.

The prerequisites, then, include an encyclopaedic grasp of 400 years of music, working knowledge of at least two dozen orchestral instruments, the ability to memorise a score containing hundreds of thousands of notes, and ears capable of detecting the slightest mishap in the sonic whirligig of a symphony orchestra going at full pelt. The great Toscanini once stopped a rehearsal, pointed at someone sitting near the back of the second violins, and said: “By the way, your E-string is out of tune”.

Then there is conducting technique - a craft that must convey speed, loudness, phrasing, articulation and mood with an elegant flick of the wrist, and must keep 100 or more wilful artistic types synchronised to the last microsecond.

But the musical side is, curiously, not even the most difficult aspect to being a top-notch conductor. When Leonard Bernstein walked into a crowded room, all eyes turned towards him as if by compulsive telepathy. The charisma needed to dominate an orchestra such as the London Symphony - full of larger-than-life virtuosos not shy about voicing their opinions - must be colossal. If you are not a born alpha male, take up the viola instead.

At the same time the conductor must be a poster-boy for the whole organisation: the personality who attracts crowds and keeps the show on the road. Conductors need truckloads of self-confidence, not least because what they are perpetrating is a confidence-trick. Although they are usually the highest-paid performers in the concert hall, they are also the only ones producing no sound whatsoever. Little wonder that, in so many cases, this self-confidence curdles into a ego the size of Belgium - prickly, preening and (when it comes to misusing their power to pull young females in the orchestra) often predatory.

You'll notice that I talk of the conductor as “him”. Sadly, in 99 per cent of the musical world, that is still the case. If a woman wants to succeed with the baton, she needs to be not just more commanding than the men around her but ten times more commanding. Yet few women want to be conductors. Perhaps they are just less prone to megalomania.

RICHARD MORRISON

Most flamboyant: Leonard Bernstein (1918-1990)

The charismatic American who led the New York Philharmonic in the 1960s lived a life of unbridled excess, combining marriage and fathering three children with a string of affairs with attractive young men.

Most temperamental: Arturo Toscanini (1867-1957)

The long-lived Italian - he started at 19 and retired at 87 - was renowned for his fits of rage. One of his diary entries reads: “This morning I was so very upset with the bass clarinet that ... I chased him out of the orchestra.”

Most mysterious: Carlos Kleiber (1930-2004)

German-born Kleiber produced arguably the definitive Beethoven's Fifth on disc, but towards the end of his life he became a virtual recluse and tried to withhold his own recordings because he was such a perfectionist.

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