David Peters, a Swiss-franc swap broker at Tullett Prebon, casts off his suit and dons red silk trunks, a white jersey, and red boxing gloves. The transformation to "Mad Dave" complete, he prepares to take on Scott "The Guvner" Gleed, a health and safety officer.

The same evening, at a makeshift arena under a railway bridge at London's Liverpool Street station, financial adviser Jon "Robo" Cobb challenges accountant Alan "The Amazing" Fitzgerald, and Jamie "No-Nonsense" Spence, a broker, throws punches at trader Mehmet "The Basha" Pasha.

"It's a massive adrenaline rush," says Peters, 42, who started boxing two years ago and fights every two months. "I'm always scared to death before getting into the ring, but then it's fantastic."

"White-collar boxing" has become so popular in London's financial district that the Real Fight Club, the first to stage such matches in the city, now has about 1,000 members and will open a gym behind Societe Generale SA's offices on Jan. 29. Rival Cityboxer.com has attracted about 300 fighters in the last year.

"If they have a bad run in the markets during the day, this is the perfect way to deal with it," says Matthew Baldwin, 27, a currency swaps broker and spectator at Mad Dave's fight.

Alan Lacey, founder of the Real Fight Club, says he started boxing when he was an event organizer for banks and "a fat, lazy guy in his 40s trying to quit smoking." The club he set up in 2001 now attracts audiences of 300 to its fights.

No victors are declared in most of the three-round bouts, because the fights aren't about winning and losing, Lacey says.

"This is an opportunity for a man to be a man," says Lacey, 54. "It's fantasy time, but mixed with reality, because even a punch at an accountant is a punch."

Fantasy time for Peters starts as he walks through the cheering crowd to the sound of Deep Purple's "Smoke on the Water." When the opening bell rings, the crowd - mostly men wearing dark suits and clutching cans of beer - shout, "Come on, Davo, forward."

Peters, in the red corner, wears gloves weighing 16 ounces instead of the 6- or 8-ounce gloves that professionals use. The gloves are heavier to soften the punches, and each round lasts two minutes rather than three.

Peters lands a few punches before he and Gleed tie up in a sweat-soaked clinch. The referee, wearing white latex gloves, steps in to separate the fighters. Two paramedics are present in case of injuries.

Just like professionals, the boxers retreat to their corners after each round, clean their mouth guards, spit into plastic buckets, and take instructions from their trainers.

"We work in a quite aggressive environment, and watching those guys beat each other up, that's what we get satisfaction from," says broker Neal Taylor, 30.

Mark "The Burf" Burford, founder of Cityboxer, entered the ring when he was 14, after he couldn't get transportation to tennis lessons.

One of his pupils is Jack Markham, 25, who helps hedge funds trade equities at Dresdner Kleinwort. Hitting a punching bag as he trains for his first fight, Markham says he has long wanted to try boxing.

"It's basic, it's raw," he says. "There are no fancy frills, and I'm looking forward to getting my head knocked around a bit."