'Ya, ya, ya, ya, ya. Twenty thousand. Ya, ya, ya. I know . . . Made a killing . . . Barbados, ya . . . Nice, ya . . . need to top up the tan, ya . . . ya, ya, ya . . .”

This is the drawback of being a commuter. Sevenoaks to London and back every day and I always end up sitting next to the pinstriped idiot who can’t grasp the fact that everyone else on the train might not be interested in his share-dealing prowess.

I’m fine with “I’m on the train, see you in 20 minutes. Bye.”

I’m not fine with “I’m on the train. No, I’m fine to talk. Got a whole hour before my station . . . Did you hear about Samantha? Really? Really? No! You’re joking! Which breast?”

Of course, you can’t ask them to shut up because you’ll be happy slapped. If only there was a button you could push to kill the conversation.

Well there is. It’s on a little black box called a phone jammer. Illegal in this country, the United States and most of the European Union, the basic version costs as little as £25 in Hong Kong. By sending out a blizzard of radio waves, the cigarette packet-sized gadget will knock out a mobile phone signal within a radius of five to 10 yards. A more expensive version can take out a whole train. Very James Bond.

The fact that it’s illegal does not seem to be deterring an increasing number of jammers. Recent reports from America suggest that demand is sharply on the increase. Despite the threat of an $11,000 (£5,360) fine for anyone caught using the device, exporters in Asia are receiving hundreds of orders every week. It seems $11,000 is a small price to pay for a bit of peace and quiet in a land where people start shooting each other when the traffic gets bad.

Two weeks ago the Wireless Association – the trade body for the US mobile phone industry – formally opposed a request by two companies to relax the federal law banning jammers. Of course they would, wouldn’t they? But it’s clear that new battle lines are being drawn. People are taking action against the blabbers, prattlers and ranters – and not just in America.

I was introduced to the world of phone jamming in the same way that a young Ivy Leaguer might be introduced to one of those masonic sects where everyone wears hooded robes and you all take it in turns to flay some nubile housemaid on an altar once a month.

I was at a cocktail party at the Foreign and Commonwealth Office when the approach was made. I had had a particularly rough commute that afternoon. The female hoodie next to me had been rapping and cussing and saying “That’s whack, man” repeatedly down her mobile all the way from Orpington to Charing Cross. Absolutely everything was “whack”, according to her.

I had arrived at the party all Prince Philip red, pronouncing furiously on the state of society today. I didn’t care, I expostulated, how disadvantaged her childhood had been, she didn’t have to take it out on the rest of us. Then came the furtive whisper: “You need a jammer.”

With a nod and a wink, I followed the dapper man to the outer edges of the party and he began to explain. He commutes from somewhere Midlandsish to somewhere Birminghamish. When an annoying fellow commuter begins to prattle, he simply flicks a switch and the prattling ceases.

“It’s like playing God,” he explains. “Sometimes, if it’s quick and meaningful, I allow a conversation. A mother calling to say goodnight to her kids. A man explaining why he’s going to be late for dinner. But mostly I don’t.”

As he sips champagne, he confesses that it has become something of a sport. His favourite game is to kill off and recreate a persistent offender’s conversations for a whole journey. Like this: “Hi Ted, so I was playing golf with Angus the other d–” Click.

“Sorry Ted, lost the bloody signal. As I was saying, I was pl–” Click.

“Blasted phone, Ted. That’s the Finnish for you. Anyway, as I–” Click. “Christ, Ted. Must be a storm coming or something. Anyway, Angus was teeing up and you’ll never–” Click. Man throws phone out of window.

Goggle-eyed, I asked for a demonstration. We spotted a mobiler in another corner of the party. We sidled up. The switch was flicked. For a while the mobiler continued to gesticulate and blab. Then he looked nonplussed at his screen: no signal. Peace and quiet. Miraculous.

In my excitement, I broke the rules of the Jammer Club. I asked if I could speak to other jammers he knew. On the record. For an article. In a newspaper. This was clearly akin to our young Ivy Leaguer turning up at the first flaying ceremony dressed as Bob the Builder. My introduction was rescinded. My contact melted back into the party. My chance to infiltrate the jammers was lost.

In the days following, I asked my less salubrious friends if they knew of these wonder things known as phone jammers. Surprisingly, two did but neither would reveal their sources.

“I’m quite happy with no one knowing about these things,” was the message passed to me from one user. “That way, I can continue commuting in peace.”

From the buzz in the technology chat rooms of the world, it is clear that the club is growing. Names of companies that import the jammers as “flashlights” are passed from one irate blogger to the next. Happy owners include hairdressers, bus drivers, public speakers and cafe managers. The Savoy cinema in Dublin installed one in 2003 but after a local paper published an article about it, the phone police turned up and insisted, on threat of a fine and imprisonment, that it be removed.

“I think it is an injustice not only to the Savoy but to patrons of cinemas all around the country,” said the cinema group’s communications manager at the time, clearly sensing that this was not just about phones, it was also about civil rights, our human rights, our freedom.

Ofcom, the UK’s communications regulator, is quick to point out that the jammers are illegal for good reason: “They cause deliberate interference to the radio spectrum which can cause a nuisance to other users and at worst are dangerous – potentially jamming the frequencies used by the emergency and safety-of-life services.”

I like the bit about causing a nuisance – an eye for an eye and all that. But the risk to safety-of-life services? Oh, come on. I’m on a train. I’m going to switch the thing on for only a few seconds to ruin Derek’s blow-the-bonus-in-Barbados chat. It’s hardly going to bring the London Ambulance Service to its knees.

And what about the health-giving properties of a phone jammer? Stress-free travel to and from work could save the National Health Service millions in reduced coronary distress. I, for one, would have lower blood pressure.

Anyway, how are they going to know? As white-collar crime goes, this is pretty hard to detect – a surreptitious black box in a suit pocket on the 8.24 from the sleepy commuter town of Chelsfield. Ofcom has prosecuted four people for selling jammers but has never caught and prosecuted a single person for using them.

I obviously wouldn’t join the jammers – I’m too law-abiding – but if any of you are going to Hong Kong in the next couple of months, I need a new flashlight.

And something that fries iPods would be nice, too.