The White Devil, Pavilion Theatre, Brighton, January 13 - February 4

So why have InService, a Brighton-based production company who met through church and started out by establishing a youth theatre, chosen Webster's The White Devil for their first professional production?

Is there a sexual aspect to her humiliation of him?" asks the fight director, surveying the improvised stage space. "Are the chairs precious or can they go flying?"

"We haven't made chair decisions yet," answers director David Oyelowo. "If you decide you want them to go flying, that's how we'll make them."

It's lunchtime in The Old Market's rehearsal area and, despite the tomato soup and Waitrose flan that's doing the rounds, the actorly activity is showing no signs of abating.

In the middle of the room a masked Israel Aduramo practises his fencing while others discuss their roles and pass round a pictorial guide to the military academy at Sandhurst. There are fragmentary debates (for one particular skirmish the fight director suggests "smashing him in the back of the head" while Oyelowo favours "disabling him with a swift kick to the balls") but the dominant mood is one of urgent collaboration.

Oyelowo's little boys are delivered for a visit and the youngest takes up residence on his dad's hip, playing with an actor's beard as the group lean in to choose from an array of flick knives and pistols. "What's the action for cocking either of these?" asks Oyelowo. "Don't you think the smaller knives are more menacing?"

One week into rehearsals and InService's production of Webster's The White Devil, still very much in its tracksuit bottoms, already looks like the most exciting thing to happen to Brighton theatre in recent history. The cast of ten, all locally-based, has been gleaned from the RSC, West End and Broadway. Their professionalism is forceful, their passion contagious and their attention to detail frankly obsessive.

Catch a snatch of energised performance and their mission statement, to "use the creatively vibrant Brighton as a power-base from which to produce world-class theatre", doesn't sound so ambitious.

Formed two years ago by five Brighton actors including Oyelowo and his wife Jessica, InService is an attempt to create a theatrical producing house for Brighton along the lines of Sheffield's Crucible or Manchester's Royal Exchange.

Following two successful productions by the Brighton Youth Theatre (which they established and run in conjunction with The Dome), InService are now preparing for their first professional production, a modernised staging of The White Devil which, in a bid to attract the attention of national critics, will run for an unprecedented three weeks.

At its helm is the 29-year-old Oyelowo who, having achieved recognition as, incredibly, the Royal Shakespeare Company's first-ever black English King (but better known to the public as Danny from BBC spy drama Spooks) is now the youngest member on the RSC's Board of Directors. He was asked to join the likes of Judi Dench, Patrick Stewart and Ian McKellen in their upcoming complete Shakespeare season but, with six films coming out, says he felt it was "the wrong time to take myself out of the loop".

In the next few months, cinema-goers will be able to see Oyelowo play a lovelorn lawyer in British rom-com The Best Man and a tap-dancer in American Blend.

He will also star with Clive Owen and Jennifer Aniston in Derailed and, with James McEvoy ("a truly extraordinary actor") in The Last King Of Scotland, a film about Idi Amin's tyrannical reign in Uganda.

Then there's the small matter of Kenneth Branagh's As You Like It, set during the Magi period of Japan, in which you'll see Oyelowo's Orlando engaging Adrian Lester in martial arts and sumo wrestling in "a very, very purple thong". And he's just finished playing a paranoid schizophrenic in the BBC2 film Shoot The Messenger. "I chase diversity furiously," he shrugs.

Now this most in-demand of actors is making his professional directorial debut, a task he has prepared for via his work with the Brighton Youth Theatre, from whose ranks he has also drawn his assistant director, Kat Drury.

"It's been a huge learning curve," he says. "You have to work out how to talk to these kids in clear terms about very sophisticated ideas. But on the other hand you learn so much as an actor from teaching young kids. Because they are not yet shackled by training there is something very raw, very real, very private and instinctive.

"What we want to create with InService is a year-round, cyclical thing whereby a professional production feeds into workshops which feed into a Youth Theatre production which then feeds back into a professional production. That combination of trained skill and youthful freedom is what makes for a great production."

In the eyes of InService, then, working with young people is a theatrical opportunity to be pursued rather than avoided, and they have fostered their relationships with members of the Youth Theatre, helping them out with audition pieces and facilitating their professional debuts. So it seems strange that a company dedicated to such wholesome ends as "combining forces" and "giving something back" should choose, for their big launch, a play so full of sex and violence that it was once described as a 17th-Century cross between The Godfather and Reservoir Dogs.

"People often ask me 'Why aren't you doing Shakespeare?'" says Oyelowo. "The answer is: 'Because you just asked that question!'

"As for all the hitting and slicing and cutting and killing, we live in an age where these kids are exposed to all that kind of stuff in computer games and films anyway. You can't patronise these young people and suggest they don't know anything about greed and lust."

Written and first performed in 1612, The White Devil, despite being one of the most sensationally grisly of the Jacobean revenge tragedies, was actually based on the true history of the famous Italian courtesan Vittoria Corombona. Plumbing the murky depths of Italian politics, Webster's unashamedly bloody plot centres around a love affair, engineered by Marcello, between his beautiful sister Vittoria and the hot-tempered Duke Of Brachiano.

Hypocrisy and revenge are unleashed by the act of adultery and in the moral chaos that ensues murder follows violent murder, threatening to destroy the escaping lovers.

"The White Devil is as bloody as it gets," acknowledges Oyelowo, "but it's ultimately a morality tale - it illustrates what happens when people degrade themselves in the pursuit of lust, ambition, power. In the hands of certain people these plays can become a celebration of evil - whereas for me it's a warning.

"It so happens we know each other because we're all Christians and go to the same church," he continues. "We aren't out to do drama that is Christo-centric, but we want to tell stories that are life-affirming, and a lot of the time the only way you can see the light is to go to the dark places.

"In a way, we're going back to plays being put on by people who had a knowledge of the spirit. I think we're able to bring a dimension that, in our secular society, is missed a lot of the time - it's almost taken out, a given that we're in a world where God doesn't matter.

"For these plays that is not the truth."

But while InService's production may draw closer to tradition in this respect, in others Oyelowo has made considerable changes: 32 characters have been conflated to 14, a sizeable portion of Webster's ornate, proverbial language has been cut to clarify the plot and, in an exceptionally bold move, Vittoria's brothers Flamineo and Marcello have become the sisters Flaminea and Marcella.

"I've endlessly spoken to actresses who say, 'All the great parts in the great plays are for men'," laughs Oyelowo. "So this was partly my perverse way of redressing the balance. It also seemed more shocking, more taboo, to have a sister prostitute her sister. And then of course there's something very powerful, very theatrical, about three sisters. It has a resonance. By having three sisters you get something for nothing."

But Oyelowo's most ingenious alteration has been to transpose Webster's characters, all aristocrats and high-ranking military types, to a Sandhurst-like setting where sword fights and poisoned pictures make way for guns and flick-knives.

In a world of strict social order the underbelly of sin and corruption can be more dramatically exposed. It also gives Oyelowo an opportunity to explore his own personal gender prejudices. "Whenever I see a woman in uniform," he declares, "I think, 'Did you have a bad relationship with your dad? What went wrong?'"

"The thing about Jacobean tragedy is that so often people think they know what they're going to get," he continues, "namely a lot of blood and a lot of people dead at the end. Which is true.

"But I felt that, in The White Devil, the horror is not so much with the killing but with what happens before - the thought and the plotting and the level of concentration these people put into trying to undo someone. I almost felt that that was worse, somehow.

"And with what's happened with Abu Ghraib, all of those pictures - it just feels like the right time to explore that connection between regimented worlds and the true nature of violence."

Tickets cost £12.50 and £5. Call 01273 709709 to book.

Two-for-one ticket offer The Guide has teamed up with InService to offer you two tickets for the price of one. This offer applies to tickets priced £12.50 (not concessions) for the following shows: Jan 13, Jan 14, Jan 16, Jan 17 and Jan 18. To claim this offer, please quote Devil when making your booking. This offer is subject to availability.