By Stephen Smith
The first rule of cage fighting is that everyone's talking about cage fighting.
Or at least that's what its promoters would like you to believe.
They claim that their uncompromising mixture of boxing, wrestling and martial arts is the fastest growing sport in the country, with thousands tuning in to bouts on satellite television and punters paying up to £500 for a ringside seat.
Unlike the white-collar, bare-knuckle scrapping of the film Fight Club, cage fighting is above board and perfectly legal, though you might find it hard to credit if you saw it.
Frankly, there are hardly any rules in cage fighting. The few that are insisted upon read like one of those signs on the wall of a swimming pool - in this case, the municipal baths favoured by the Bash Street Kids.
"No gouging, no elbows on the spine, no fishhooking...". (Fishhooking, in case you're wondering, is the practice of putting your fingers in your opponent's mouth and tugging it in ways which nature never intended).
The Queensberry rules, it ain't. But that's the point, of course.
Cage fighting offers visceral thrills - indeed, the prospect of actual viscera - at a time when a tag team of corporate money and health and safety regulations appear to have knocked the stuffing out of other sports and pastimes.
The promoters say they are attracting fight fans away from regular boxing.
To hear them tell it, the noble art is so down and out, you could sell advertising on the soles of its boots.
But boxing promoter Frank Warren was having none of it when Newsnight spoke to him.
"It's not a threat to boxing," he said. "It's not for me, watching a bloke kneeing another in the cobblers? No thanks."
"A boxer is always the most famous sportsman in the world - you ask the average man on the street to name a cage fighter."
Top of card
James "The Machine" McSweeney might be the first British contender in the new dispensation to gain a following.
A useful footballer in his youth, he now merits a slot towards the top of the card at a Cage Rage event in Wembley Arena.
In the ring, he gets the job done, as the expression goes. He's duly methodical en route to victory.
But in his dressing room after the bout, we encounter a young man who is solicitous, almost courtly, in his manner.
McSweeney - it's impossible to refer to him by his steely nickname - is touchingly gallant to his partner, with whom he's just been reunited after a self-imposed separation of a fortnight.
Before a bout, the fighter removes himself from the entire female side of his family, in fact from anyone who might bring out his tender feelings.
He won't thank me for saying so, perhaps, but he's so in touch with his feminine side that he has to cut himself off from it in order to concentrate on the hairy-arsed business of fighting.
McSweeney's monkish training camp is all of a piece with an almost hysterically butch fitness regime.
"I drag sledges with weights on up hill," he tells me.
"I pull tractors."
I almost expect him to say that he stops locomotives with his upraised palms.
McSweeney has a chance of making a living out of his flying hands and feet. By contrast, most fighters have day jobs, as farmers, say, or bouncers.
They are attended by a fully qualified doctor, a GP who takes the pragmatic view that cage fighting will go on whether or not he is around to unstopper the smelling salts and suture the wounds.
The promoters of the sport say there are no recorded cases of brain damage among contenders, though they are in no position to say what might emerge in 20 years' time.
That's not good enough for Bob Blackman, a Tory member of the London Assembly whose constituency includes Wembley Arena.
"I'm a libertarian. What two grown men choose to do to each other is their own affair, but I'm concerned that cage fighting glorifies violence.
"It's only a few steps away from the gladiatorial contests of Ancient Rome."
Mr Blackman's misgivings are shared north of the border, where pressure is mounting to scrap a cage fighting event next month.
We invited sports psychologist Ellis Cashmore to cast his eye over the sport.
"Sport was meant to be exciting, and this is," he said.
"It's raw, it has the feeling of being underground, and that's part of the appeal. Once that's gone, it's finished."
Stephen Smith's report appeared on Newsnight on Thursday 19 July at 2230 BST on BBC Two.