How do you reinvent the world's most successful movie franchise? That was the scary task that faced the director, writers and actors on 'Casino Royale'. Johnny Davis meets them and reveals why it took grit and guts to complete the film

The chips are down at Casino Royale. The makers of the 21st James Bond film are about to see if their gamble, the biggest in 44 years of the world's most successful movie franchise, has paid off.

"To be honest, I'm nervous," says director Martin Campbell. "Now I've got to release it to the wolves. I'm waiting for the Sword of Damocles to fall. The bigger the gamble, the bigger the win? I think so. The Broccolis [family of long-time Bond producer Albert "Cubby" Broccoli, who died in 1996] were adamant we had to change it; we had to go back to naked Bond. I totally agreed with them."

On paper, the idea of rebooting Bond for the 21st century makes sense: post-Austin Powers, brittle and fiery is how we take our spies. Jack Bauer, say, or Jason Bourne. Other pensionable heroes, Superman and Batman, have been successfully reinvigorated. But they needed fixing. Bond wasn't broke.

His last outing, 2002's Die Another Day, added the biggest-ever gross to a series total standing just shy of £4bn. ("The only good thing about this picture is that we can only lose $800,000," complained one executive on Bond's 1962 movie debut, Dr No. No wonder Campbell's got the jitters.)

But Casino Royale is a fresh start. It sweeps aside Moneypenny, Q, the cackling megalomaniacs with their underground lairs, the silhouetted dancing girls and - oh, yes - the invisible car. This is back-to-basics Bond, the character Ian Fleming introduced in the first book, in 1953. Newly graduated to his "00" status. Unrefined. Lean. Hungry. As M (Judi Dench) describes him in the film: "A blunt instrument". "He's a different Bond in every way," says Campbell.

Yet, as anyone who's only seen the trailer will surely attest, Daniel Craig is an inspired choice. Admired for playing charismatic tough-nuts in Layer Cake and Munich, and with an allegedly ladykilling personal life linking him to Kate Moss and Sienna Miller, his CV would seem ideal.

"To begin with, you think: this is a little strange - is he really James Bond?," says one of the film's screenwriters, Robert Wade. "Then, after 10 minutes, you think: was there ever anybody else?" "He's a very good actor," says Wade's writing partner Neal Purvis. "He's put a hell of a lot of work in. Plus, lots of the criticism of him as Bond was internet nonsense. If the internet was around in the 1960s, then George Lazenby would have had a terrible time."

With 200 actors apparently considered for the role, some reasonable enough (Hugh Jackman, Jude Law, Ewan McGregor), some perhaps less so (This Life's Jack Davenport?), Craig auditioned the way everybody else did - by doing the From Russia with Love scene where Bond emerges from his bathroom wrapped in a towel and brandishing his Walther PPK, to find a stranger in his bed. It's been the screen test for every would-be Bond since Sean Connery. "It's tradition," Craig explained recently. "If [producer] Barbara [Broccoli] hasn't destroyed that piece of film yet, I hope she will soon. I don't want anybody to ever see it."

Filmed in four countries and on 40 sets,Casino Royale was a punishing 118 days of six-day weeks, starting in mid-January and ending on 18 July this year. Make that seven-day weeks if you were Campbell.

Meanwhile, action fans have little cause for concern: they're likely to come away from Casino Royale impressed. More visceral than any previous film, here's where we see Bond bleed.

And Craig got stuck into the stunts himself, splitting knuckles and getting a cap knocked out for his trouble. One sequence finds him getting so battered that the wardrobe department was obliged to produce 25 suits, in various stages of wear and tear. This time round it's CGI out, fistfights in.

"I think in the last film, the climax took place on a burning 747," smirks Campbell, who also directed 1995's Golden Eye.He catches himself. "Which is fine for that movie. But, if you've read Casino Royale, it doesn't fit. It's a much darker, more realistic book."

"There was no way you could top the last movie," says Purvis. "It would become a cartoon if it went any further over the top."