Off screen, Carlos Bernard and Kiefer Sutherland, the actors who play Tony Almeida and Jack Bauer, the apparently un-killable counter-terrorism agents in 24, are the best of friends. With that slow, almost whispered drawl familiar to the squillions of 24 fans around the world, Bernard describes their relationship: "Let me put it this way. I had a party at my house the other night, and Kiefer was the last person to leave, at five in the morning."
On screen, it's a different story. During the first six seasons, Tony and Jack couldn't have been closer, saving each other's lives countless times. But all that has changed in the seventh season, which is released this week on DVD and Blu-ray, in which Tony, back from the dead and eaten up with rage about the murder of his beloved wife Michelle, teams up with a dastardly terrorist cell. Tony has – apparently – joined the dark side.
In typical 24 fashion, this terrorist group are bent on destroying America, and only one man can stop them: Jack Bauer. Boasting more twists and turns than the average Alpine road, the seventh series makes for a fiendishly addictive ride.
Sutherland has said that the format is the real star of the show (whose fans include Dick Cheney and Barbra Streisand) – it is set in real time over 24 hours – and it's true that it only makes it more compulsive. I watched the latest season in an unstoppable frenzy over just four days.
In person, Bernard is the opposite of Tony. Where the character is broody and moody, the actor is chirpy and cheerful. He even – and this will shock aficionados of the scowling agent – has an infectious laugh.
The 47-year-old actor, who is married to actress Sharisse Baker and has one daughter, Natalie, locates Tony's emotional position at the start of the seventh series. "He's a very damaged individual. He's been through a lot and lost a lot. He is really angry at the system he had dedicated himself to fighting for over so many years.
"Tony has genuine, intense feelings for Jack. Because of what they've been through together over the years, he has a lot of love for him. They're like brothers. But sometimes when brothers get into fights, it's worse than anyone else feuding because of that very intensity of feeling. If Tony had had it his way, Jack would not have got involved in this case – he would have stayed away. But Tony couldn't stop it. Jack is always sticking his nose into things!"
The fact that Tony switches sides did not go down well with 24's fan-base. "People were furious," Bernard smiles. "It was tough for me to go out for a coffee. I'd get a lot of 'I'm really mad at you!' And I'd think, 'do I know this person? What did I do to him?' But I'd hate it if they didn't care. There is nothing worse than eliciting boredom. You can be bad or you can be good – just don't be boring."
Tony's allegiances are not the only thing to shift during this series. There has also been a change in the show's portrayal of torture. Over the past few seasons, even fans have expressed disquiet about Jack's use of torture.
The bestselling author Stephen King, a fan, spoke for many when he observed: "There's a queasily gleeful subtext to 24 that suggests, 'if things are this bad, why, I guess we can torture anybody we want! In fact, we have an obligation to torture to protect the country! Hooray!'"
Other voices were even more disapproving of a show that featured 67 scenes of torture during its first five seasons – a much greater number than any other TV drama. Melissa Caldwell of the Parents' Television Council, declared: "24 is the worst offender on television: the most frequent, most graphic, and the leader in the trend of showing the protagonists using torture."
But now Barack Obama has replaced George Bush in the White House, and we are living in a post-Guantanamo Bay, post-Abu Ghraib universe. Jack would appear to be the last water-boarding dinosaur still walking the earth.
The producers of 24 have made it clear that he is a man whose uncompromising methods are seriously out of date. The seventh series opens with Jack facing trial for human-rights violations. Throughout the season, he is upbraided by a play-it-by-the-book FBI agent for his brutal approach to interrogation.
Bernard says Jack is now seen as a man out of time. "It reflects the change in attitude in the US. It's important we addressed that – it's become such a large issue in our country and you can't be casual about it. But just because in one episode Jack killed his boss, it doesn't mean we condone killing your boss. It's the same with torture. Just because Jack often tortures people, it doesn't mean we condone torture."
The actor adds: "There has probably always been this battle about how you extricate information from people. It will see-saw back and forth throughout history. It was purely because of 9/11 that it started to be OK. I don't want to say it is OK, but we began to soften our view of it because of the shock of that event. I'm sure we'll hit a time in the future when torture is seen as OK again."
The events of September 11 2001 nearly caused 24 to be axed before it had even begun. "9/11 happened when we'd only shot six episodes of the first series," Bernard recalls. "We were sure the show would be cancelled. We thought, 'Jeez, they can't put this show on air now'. But people were really engaged with the issues, and it went out. It's ironic that the terrible climate of the world actually helped the show."
Bernard could tell me if he is appearing in the eighth series of 24, but then he'd have to kill me. All he can say is that, "the future for Jack can't be good. He's never in good shape!" Does that mean that, like Tony, he might turn out to be a baddie? "I don't know if people could take that – they had a hard enough time with me!"
Over the past eight years 24 has become a worldwide hit and catapulted Bernard to stardom – evidenced by the obsessive fans he now attracts. "The other day, I found a British woman by my trash-cans," he says in bemusement.
"Her husband was waiting across the street, and she told me, 'this is one of the places we wanted to come on our visit to the US.' I thought, 'why is my trash on your itinerary?' Then she asked if she could take a picture of me. I replied: 'On one condition: that you don't go on the internet and tell people where my trash is!'"
Bernard's only other worry is that he might be forever pigeonholed as Tony. "The show has given me a huge profile, but it does limit you as well. People talk about typecasting, and unfortunately that will happen if you have success. But that's not necessarily a bad thing.
"One thing I love about this career is that it never ceases to be challenging. For your next job, people aren't going to open the door for you. You'll have to kick it down. Perhaps I should ask Jack to help!"
The seventh series of '24' is released on DVD and Blu-ray this week