Barely an hour after Special Commandant Ian Miller has run me through precisely what one can expect from some sectors of the great British public when you are dressed up as, to all intents and purposes, the enemy, and I am seeing it for myself, up close and in the rather frazzled flesh.

Though we are on the comparatively calm streets of the City of London, upwardly mobile Fleet Street to be precise (and one clear travel zone away from proper miscreant youth), a couple of inebriated businesswomen are giving us some verbal, which is giving me at least – if not the implacably calm trio of Special Constables within my company tonight – the needle. The one who just moments earlier had peed in an alley rather than use the fully-functioning nearby WC, is now blowing cigarette smoke in our faces, while her friend chats airily on her iPhone to someone she insists is her "counsel". But Miller, a former chartered accountant by day and a Special Constable of 30 years' standing, is used to dealing with her type.

"We get a lot of drunk and disorderlies around here," he tells me later, referring to the financial hub's dense proliferation of pubs and bars, and the pissed-up suits that regularly spill out of them. "And alcohol always does make everyone so much more ... well, bolshy."

The call, when it came over the police radio five minutes previously, was an undeniably exciting one for me, a first-time and strictly temporary so-called Special, here to get a flavour of one of the more seemingly worthwhile acts of voluntary service available to us today – keeping our streets safe. Police radio reported that two women were being held by a taxi driver in his black cab, the very same cab they had hoped to make a quick getaway in without paying their bar bill. Miller promptly switched on the flashing lights and the pulse-quickening Nee-Naw, and executed an impressively neat U-turn as suddenly the Highway Code became redundant to us. We raced – but carefully, mind – through successive red lights before pulling up abruptly on a double yellow, and bounding out in a manner more restrained than Bodie and Doyle perhaps, but only just.

"We've done nothing wrong!" slurs the alleyway urinator, a power-dressing late thirtysomething full of white wine and indignant opprobrium, and with, she boasts, a background in law.

"That's not what the bar manager is telling us," Miller responds.

What happens next is, in truth, somewhat disappointing, if only because it isn't the stuff of, say, The Wire or even Life on Mars. Nevertheless, it forms an integral part of what being an SC is all about: dealing with the minor offences of the drunk and disorderly. These two women, three sheets to the wind but claiming otherwise, are coolly tolerated by Miller and his colleagues, Special Superintendent Darren Sevket, a project manager for Barclays by day, and Special Sergeant Jonathan Frost, who works in marketing. Between them, they patiently but firmly convince the pair that settling the bill of £35 should be infinitely more appealing to them than the alternative: a night in the cells. After more expulsion of cigarette smoke, and a few bored expletives, an American Express is reluctantly handed over, and the bar manager is at last a happy man.

As we climb back into the car and filter into the early- evening traffic, we learn via police radio that that was the 10,171st incident requiring police intervention in the capital since the previous midnight.

"People like to keep us busy," smiles Darren Sevket.

Though it may be difficult for many of us to comprehend why anyone would willingly choose to become a voluntary representative of a profession many people openly mistrust, or even downright loathe, an increasing number of us are nevertheless doing just that. There are, perhaps, two main reasons. The first is purely humanitarian, people wanting to give something back to a community that has served them well; the second, bluntly, is likely to include a thrill-seeking element. Few jobs allow us much power and influence over our fellow man. This one does.

Currently, England and Wales boasts 14,000 voluntary constables who collectively work 2.8 million hours of duty a year. But the Government is now overseeing a recruitment drive that hopes to push that figure up to 20,000 within the next two years, ideally in time for the Olympics.

It is perhaps unsurprising that the Government is so keen to bolster a perennially understaffed police force in this way: Special Constables, even once training and uniform costs are taken into consideration, come cheap. The first two years of an SC's life costs the tax payer just £3.60 an hour, which later drops to £2.40. Little wonder, then, they want more of us to sign up.

"What makes for an ideal Special?" asks Darren Sevket, who runs training courses here at Bishopsgate Police Station. "Well, in theory, everyone."

So long as you don't have any outstanding warrants against your name, and you are a British or European citizen and a British resident, he continues, anyone over the age of 18 and a half can become a Special (there is no upper age limit). You can be black or white or somewhere in between, male or female, gay or straight, even transgender.

"Special Constables work hard to represent the very public they serve to protect," he continues. "So as much as possible, we want our SCs to represent a wide cross-section of those very people."

Though SCs are frequently called upon to help the regular police force in times of need – as at the recent G20 riots, for example, or after 7/7, for which London's SCs won an award for team effort – many of their duties revolve around fairly unglamorous grunt work, pounding the beat in highly visible numbers, thus making the public feel safe and allowing "real police", as The Wire would have it, to get on with the highly time-consuming business of building cases and seeing them through the protracted process to court, and ultimately conviction. But though they frequently work in harmonious tandem, not all "real police" are automatically respectful of their voluntary counterparts. And this, says blogger-turned-author PC Ellie Bloggs, whose 2007 book, Diary of an On-Call Girl, documented life as a police officer with unflinching honesty, is because they are, in effect, mere "hobby bobbies".

"Most of them work just one day a week," she says, "so how could they be anything else? To be completely and brutally honest about it, there is sometimes the perception within the regular force that a lot of them have just joined up solely to swan about on their days off in uniform, and have a bit of power." She laughs. "That's not necessarily a negative, though. A lot of real officers also joined for that very reason."

Ultimately, however, they are rarely cut from the same cloth, she argues, and therein lies the problem common to all TV police dramas: assumed superiority versus presumed inferiority.

"Not all police like them, no, it's true," she says. "Special Constables cannot follow cases through to court, for example, and so they cannot really help with investigations. And many Specials can't even take statements properly because they don't know how to. If you can't take a statement, then you don't fully understand the law."

And sometimes they can make snap decisions that end up making more work for the regular force. "That can strain relations," she says.

That said, she does admit that they can be a valuable extra pair of hands. "They are unfailingly enthusiastic. And they do like to arrest. And because the job is voluntary, there is no shirking among them. Would I be happier to see more of them out on the streets doing just that? Why not? The more the merrier, I say."

I tell her I'm surprised so many people are willing to do what is a potentially dangerous job. Is it not counterintuitive to sign up for something that puts us in the line of sometimes very real fire?

PC Bloggs smiles. "Skydiving is dangerous," she says. "Look, people become SCs because they get an adrenalin kick from being in a uniform, from driving around in a car at speed, and from arresting someone. If you turn up at a scene, all eyes suddenly fall on you, and on what you are going to do next. If you don't like that kind of attention, you are very likely in the wrong job."

Skydiving is certainly easier to train for, however – because anyone interested in becoming an SC isn't going to become one overnight. The training process takes two full years, a succession of mental and physical tests held during the evenings and most weekends. Here at Bishopsgate, they take on just 12 new recruits a year, and of those who do apply, a mere 10-12 per cent will pass. Successful recruits are then expected to give at least 200 hours of duty each year, which translates to approximately four hours a week, usually an evening shift between 6pm-11pm. But many SCs, Ian Miller says, go on to do much more than that.

"It's addictive," he admits, "and for so many reasons. There is an undeniable sense of giving back to the community, yes, but it is also fascinating and richly rewarding work, and a wonderful leveller. Friendships develop here between, say, a barrister and a cleaner, where in their day jobs their paths wouldn't even cross."

And what of the adrenalin rush that comes naturally with the job?

Miller, a Scot handy with firearms, smiles. "Of course," he says. "Why else do you think I still pound the beat 30 years into the job? It's not because I have to. I want to."

After my brief overview of Special Constable training, we head out on to the streets. I am not permitted to wear the regulation police jacket myself, which means that access to the Asp (the modern telescopic truncheon), a pair of handcuffs, and a can of CF spray that can do to the eyes and nose what an industrial flame does to a candle, remain safely out of my reach. I am, however, instructed to wear a reflective windcheater with the word POLICE on the back, and by simple virtue of donning it, I am no longer an ordinary citizen. I feel taller already.

Twenty minutes after we have dealt with the drunken women, we are called to a pub in Moorgate where another couple of drunks, these two male, are refusing to leave the premises. En route, Darren Sevket explains that though alcohol can frequently turn people violent, the SC's best defence is invariably the uniform itself.

"It immediately calms most situations," he says. "Even people who profess not to like the police ultimately respect us, or at the very least fear us. Either way, they see us and most of the tension falls away."

This is certainly true right now. The moment we enter the pub, a palpable hush falls on proceedings. The drunks become instantaneously passive under our gaze and readily agree to leave, issuing apologies as they do. Over at an adjacent table, meanwhile, four women have become utterly rapt by our very presence, and one of them affords me a smile of unambiguously lascivious intent. This is what PC Bloggs meant when she talked about the power of the uniform. I am sorely tempted never to remove it again.

The rest of the evening passes without major incident, an unfortunate state of affairs for the over-eager first-timer, but then as Ian Miller explains, "it's pouring down with rain, and rain reliably postpones most people's intent to break the law". On many such quiet nights, he says, they are frequently called to help with regular police operations in neighbouring Tower Hamlets, a neighbourhood of London that sometimes needs all the lawful assistance it can get. But not tonight they don't, and certainly not with a novice like me on board.

Shortly after 11 o'clock, he drops me off at Liverpool Street Station just as the surrounding pubs are closing for the night, and turfing out the tipsy and the paralytic. Almost immediately, I spy on the concourse a drunken middle-aged man in a pinstripe suit shouting abuse at a member of train staff, exhibiting all the classic signs of public disorder. His face is bright purple.

Though I am no longer wearing my hi-res POLICE jacket, I do still have my station visitor badge pinned to my lapel, which at least gives me a whiff of officialdom, a whisper of Clark Kent inclination. As I watch the argument unfold, the man raising the kind of fist he is more likely to shake than throw, the impulse to intervene becomes unexpectedly strong.

Earlier in the evening, Ian Miller had told me how this job could get under one's skin. He's not far wrong.