Babylon launched on Channel 4 earlier in the year when the pilot episode directed by Danny Boyle kicked in our front doors and tasered us in both the brain and the funny bone. Now Sam Bain and Jesse Armstrong's caustic and multi-layered police-based comedy drama is back for a six-part series.

Below, stars James Nesbitt, Nicola Walker, Paterson Joseph, Bertie Carvel, Jill Halfpenny, Adam Deacon and Jonny Sweet talk about their roles in the show...

Hello. Could we aks you to introduce your characters...

James Nesbitt: I play the Commissioner of the London Police Force, Richard Miller. He's an imposing, charming, authoritative man who's worked his way up through the police force. He started in Northern Ireland; he was probably in the RUC in very difficult times in the mid-80s. He was probably quite progressive, and remains progressive. He was likely to have been involved in the peace process. He's a man with ambitions to change the police force and take it into the 21st Century. He's someone who is forceful, and has to deal with the pressure of the most challenging job in policing. There's also another side to him, and his personal life is hugely under pressure.

Nicola Walker: I play Assistant Commissioner Sharon Franklin. She and the other Assistant Commissioner in the story, Charles Inglis [played by Paterson Joseph], have quite a complicated relationship. There's always that thing that they'd both want the big job, if it ever came up. So that's quite difficult - that's always there. Paterson and I used to talk, off script, about whether or not they'd known each other in their training, and we decided that they definitely had - there's a lot of history there between the two, so that was quite fun. She comes more into her own in the second half of the series. She's quite low key at first, until she catches Liz Garvey's [Brit Marling] eye, and everything starts to change.

Paterson Joseph: I play Charles Inglis, Deputy Commissioner in the London Police Force. Charles is ambition and tough. Cynical on the surface but with hidden integrity.

Bertie Carvel: I play Finn Kirkwood, the Old Bill's answer to the Dark Arts. He's cynical, aggressive, intelligent, hot-tempered - but his spiky armour conceals a heart that beats with a passion for public service and social justice.

Jill Halfpenny: I play Davina, who's in the TSG [Territorial Support Group]. She's married to Banjo, who's in the Armed Response Unit, and she's a really no-nonsense, straightforward, in-yer-face kind of woman.

Adam Deacon: I play Robbie. He starts off in the TSG, and he's quite a loud character, a guy who really wants to be heard. He manages to cheat his way into armed training - which is a big dream of his. He goes through training, and you follow his journey into the Armed Response Unit. And obviously he has to change. He's not the top dog any more in the van, and he has to calm his banter down a bit. He's growing up a lot as well.

Jonny Sweet: I play Tom Oliver, who is essentially Richard's little servant. He's done some sort of graduate trainee scheme, hurdled all of the boots-on-the-ground experience usually necessary to enter the inner sanctum of high command, and is now ricocheting between his intense fear of Richard, habitual administrative errors, and serving as Finn's bullied scapegoat. He's a frightened div-boy who is leagues out of his depth.

What was it that attracted you to the project?

Jonny: Obviously the main pull was the holy trinity of Sam Bain, Jesse Armstrong and Danny Boyle. I am not only a fan but also a kind of student of Peep Show, and the pilot script was really amazing.

Jill: Honestly, it was everything. When you get the list through of who's involved, from exec producer to director to writers, it's a bit of a dream team. So it was everything. And then, on top of that, I read the scripts, and I loved the character. It was refreshing to play somebody like that.

Adam: For me, it was so many different things. On a personal, acting level, I was waiting for a part like this. Since I won a BAFTA [Rising Star] award, I was getting offered the same kind of thing all the time. It was all drug dealing parts, or street kids, people on the wrong side of the law. It was quite a scary time, because I was turning down a lot of work, and as an actor, you want to work. But I kept my faith, and people kept telling me something would come up, and all of a sudden I got this casting. And I have to be honest, I thought it was one of those castings that I wouldn't get, because of how big it looked on paper... the fact that it was Danny Boyle, and Sam and Jesse writing it. I didn't think they'd see me as a police officer, because I've always played the other side. But I went to the casting, and a week later I got the part, and I was over the moon.

Whenever you switch on the TV, there's a police drama on. But this is very different from all the others, isn't it? Was that part of the attraction for you?

Paterson: It is a typical police show, in that the cops are dealing with crime. The difference is that the cameras are turned on the inner workings at the top. This bird's eye view of policing London is absolutely unique and was a major attraction for me in taking this role on.

Bertie: Yes, it's a really three-dimensional look at the politics of policing. It looks at the whole ecology, as it were. It's certainly not just cops and robbers.

Nicola: Yeah, I think that's the attraction for everyone involved, both behind and in front of the camera. We're all televisually very savvy these days, whether you work in TV or not. We're all used to seeing a lot of cop shows, some of them brilliant, some of them very generic. But it seemed to all of us that no-one had actually done this before, where they were approaching this world as it's slowly being born into this new era of transparency. Of needing PR. The old days, where the police had special relationships and offered little backhanders to certain members of the press, have been blown out of the water by the internet and new media. This huge beast of an establishment has to open its doors up, and that's what this drama is all about.

James: It was the writing, really. That was the attraction. And the fact that it felt like something I hadn't really done. It felt very much of its time, very different from formulaic police dramas. Not to say that a lot of them aren't very good. I've been involved in cop dramas myself. But what was attractive about this was, of course, Danny [Boyle] at first, and Sam and Jesse's writing, and then when it was taken on as a series, Jon S Baird was hugely important to me. He's a brilliant, collaborative director. It was like nothing I'd seen. I think Miller is an extraordinary man. Often what you try to do is create ordinary people in extraordinary circumstances. I think this is an extraordinary man in extraordinary circumstances.

What do you think are the chief strengths of Sam and Jesse's writing?

James: Clearly I knew their work before. They have natural quite dark humour, and they're constantly evolving. They created a very rounded, complex character in Richard Miller. I think their observation of how policing is changing, and communications are changing and the news is changing, is very acute. I think their voices are very original, and they marry humour and drama together very well. They create very good characters, but they also will occasionally throw in some very funny lines as well.

Nicola: I'm a fan. I came to the audition as a fan on so many levels. For me, it's that they dance a very delicate and beautifully constructed line between comedy and drama. And they ask a lot of their actors. It's all in the script, though. If you just do what you're told and say the words that they've written, you will be going the right way. That's what draws me to their stuff.

Paterson: Sam and Jesse have always been able to marry dramatic situation with a twist of the absurd. They've added depth and tension to the mix and the result is a notch up from anything I've ever seen them do.

Bertie: Their wit and dexterity of thought float on top of dramatic writing with real emotional and intellectual depth. They have an extraordinary ability to be funny and serious at the same time.

What did you do in the way of research for the role?

Bertie: It's really all in the script. But, you know, I read the newspapers. I've always been interested in current affairs and paid fairly close attention to the stories of the day. My father is a journalist, as was his father and his grandfather before him, so I suppose that's sort of in my blood. You'd have to be living on the moon not to have picked up what a hot topic press PR, spin-doctoring and information management have become in recent years. The argument that's at the centre of Babylon is a really important one for our times, so it has helped to have a strong sense of the context.

Jill: Actually, when we did the pilot, with Danny [Boyle], we did quite a bit. We had a lot of people coming in and chatting to us. We got taken to Gravesend to do some riot training with the police. We read books, we watched documentaries, and everything was made available to us if we wanted it. Danny gave us access to all of that.

Adam: We were really lucky. Danny Boyle was a great believer in doing a lot of research before we got on set. That's great, not a lot of directors work like that. Normally it's a real rush, you get your script maybe two days before and you learn your lines. With Danny, he made sure we had enough research. We had DVDs, documentaries we could pick up whenever we wanted, a lot of training in Gravesend. Especially for me, because I had to train with the Armed Response guys as well. So I got to shoot the guns and everything. It was really good fun, to be honest. And we also got to talk one-on-one with a lot of officers. It also helped with dialogue, just to check if police really did talk in a certain way, and would use lines like this.

Jonny: We met some high-ranking ex-police fellows, who were incredibly interesting, insightful and forthcoming about the pressures and institutional snags and eddies of the police, but sadly I wasn't afforded the opportunity to tear around a faux gang-land hang-out made of chipboard firing blanks at wooden cut-out enemies. I'm hoping Tom's character will develop sufficiently in the future to necessitate more of that kind of vibe.

Has your opinion of the job that the police do changed as a result of working on the show?

James: Yes. I think that's an important question. I think publications beforehand, particularly on the right of the political spectrum, might have thought that this was going to be a police-bashing exercise. And I think, if anything, it's the opposite of that. I think I've taken from it the enormous difficulty the police are under. Of course I'd seen that, growing up in Northern Ireland. But I think nowadays, with the fact that everyone is a news cameraman, it makes it harder than ever...

Cameraphones are slightly the bane of my life, but they're certainly the bane of the police's life as well. When we filmed in Miller's office, I'd stand there and look out over the whole of London, and it was very helpful in reminding you of the impossibility of that job, of trying to govern and protect an entire city. Of trying to make the right decisions when there are those in politics who are against you, and the public are against you. But one of the things that it was important for me to remember was that kids still want to join the police when they grow up, and that says something about the police. That doesn't seem to have been lost.

Nicola: I completely respect the job our police do. I knew nothing about this level of it before. I had a very funny incident happen to me after the pilot episode went out. Standing getting some money out of a cash machine, I felt someone behind me, and I turned, suspiciously, like many Londoners do, and it was an armed police officer in full gear. And I went "Oh, I don't have to worry about you being there." And they pulled up in their van and said they'd watched Babylon and really enjoyed it. And I said "I'm sorry, I don't have anything to do with the boots on the ground, I'm one of the top brass." And he said "Yeah, you're one of the top brass, you don't know what's going on." We spoke to some people who are or were really high-ranking in the force, and the respect I have for what they do is enormous. The amount of pressure they are under. One man, who's retired now, said the things he misses are the chronically stressful situations, which ordinary people would run away from. That's when he would step forward. It's just a completely different mind-set.

Paterson: Babylon has definitely added a degree of sympathy to my opinion of those at the top of the major police forces in the UK. Their challenges in a digital age, to keep us safe but keep us totally informed, are monumental and unenviable. At the same time I think they need to truly work on being transparent about their major flaws: Racism, sexism and bullying.

Jill: I think what's changed for me is I'd never really considered the level of criticism that they come under. I'd probably been the one criticising before. I'd never really thought about the impact that would have, not only on them, but on their families as well. Even down to their children, who probably go to school the next day and have comments made to them about something that was on the news the night before. It's a really tough job. But with the police I've spoken to, and in the books that I've read, it seems to be a compulsion for them - policemen and policewomen just have it in them. That's what they want to do, and that's why they put up with it.

Adam: I think they're in a really hard place. Obviously we need protection. But for the Armed Response guys it's particularly hard. If they do their job, they're going to get blamed, and if they don't do their job, they're probably going to get blamed. I think they're in a hard place. But in doing this, and in making a documentary a few years back called Can We Trust the Police, I just think a lot of the police officers out there are confused. A lot of them want to do the best they can, but they feel like their hands are tied by the government. But I think there's good police and bad police, the same as there are with any job.

Jonny: I think I probably had a vague instinctive distrust of the police before, which was founded on very little. I don't think this show assuages that entirely but I think it's given me a more complicated sense of why the police is like it is, and how for ninety per cent of the time people are trying to do the right thing.

Babylon is on Channel 4 on Thursdays.