'I remember years ago writing one of the first stories about Bertie and Celia. A week later I was at a book launch and I saw Bertie Ahern. He clocked me, and was making a beeline for me, and I thought, 'Jesus what's going to happen here?' Bertie said, 'Hiya Paddy. I remember you used to write industrial-relations stories for the paper. I've just been made responsible for labour, so if you want to talk about anything, just give me a call. Here's my number.' He didn't even mention my story. My jaw was just hanging off me. It was the first time I realised what a calculating professional he was."

Not everyone deals with Paddy Prendiville in this measured way. Headed by Prendiville and overseen by owner John Mulcahy ("He's the quality control"), the Phoenix is a news magazine, satirical rag and scandal sheet in one. A typical issue features a photo of public figures uttering piss-taking speech bubbles ("We learned a lot from Private Eye," admits Prendiville), news stories that detail the hypocrisy and internal rows of businessmen, politicians and media pundits, and plenty of straight satire. For 27 years the Phoenix has been annoying public figures with its less-than-reverent attitude, and for over 25 of these Prendiville has been at the helm, trying to find, as he puts it, "the story behind the story". Up in its poky, top-floor Baggot Street offices, he has just posed for photos against a massive desk, and is relieved to have put another issue to bed. He's telling me about how some people deal with negative coverage.

"Irate phone calls are rare," he says. "Because generally people know that there's no point. But if I walk into a room, you'll find certain people bristling. Politically it's the smaller parties who take it hardest. The PDs couldn't take criticism of any kind and Sinn Féin are difficult, probably because of the history of their organisation. The bigger parties, by and large, tend to say, 'That's life, that's the media.'"

It's not quite "the media", however. The Phoenix has always prided itself on a slightly more angled approach than the rest. "Early on I remember being asked by my boss, 'If you were going to do a profile on the minister for posts and telegraphs who would you talk to?' and I said some pretty banal things like 'the leader of the opposition' and 'the people around him'. And he said, 'No, you go to the guy in his cumann who hates his guts; the guy who lost out in some faction fight a year earlier. That's who you go to.'" He laughs. "When people ring here apologetically and say, 'I've no grudge against this person, but...' I say: 'Don't be ashamed! Grudges lead to stories!'"

He stresses that most of the stories actually come from the staff's own hunches rather than impromptu phone-tips, but sources are clearly very important and are tightly guarded. The Phoenix phone number is printed in the magazine accompanied by the words "no caller ID" so as not to scare off more timid whistleblowers, and Prendiville says that people would be "very surprised" at some of the people who regularly contact the magazine. "You do have to keep a healthy distance," he says. "There's a danger with sources. Are you going to become the prisoner or the warden? I remember losing some pretty serious contacts in the past. At least one person who subsequently became taoiseach had been pretty friendly with me until an irresistible story came up and I lost that contact."

He must be constantly tiptoeing around legal issues. An issue in?February this year had to be withdrawn for reasons he says he can't go into. "Oh, we're very careful. We always make sure to check what people tell us. Obviously, if it's malicious and without substance we don't print it. I always say when people ask me about the Phoenix and libel, that you could be writing for the Kerryman and be in just as much danger, because the libel laws are so severe. It's a bit more dangerous for us because we're writing critical stuff, but the fear is taken out of it by rigorous vetting. There's a lawyer in here checking every line and comment. 'Can you prove this? Is this true? What if he sued?' And it's always something you didn't think of that gets you. I remember a front cover, I won't say which one, but we had a huge row about running it on issues of taste – it involved being unpleasant to a woman – but we forgot all about the libel potential. We'd argued about whether we were being tasteful, but we missed the libel, and boy did that come back on us. That said, nine out of 10 solicitors' letters are try-ons. The solicitor often knows very well that there's no case, but the client thinks there might be."

Prendiville's relative fearlessness may have something to do with his politics. He has an unusually radical background for a journalist, with a former involvement in far-left and republican activism. Born in Manchester but raised and schooled in Kerry, he says that 'five to 10 years' doing manual labour in his 20s radicalised him.

"I came from a comfortable middle-class background but I dropped out of college and went to work in London," he says. "I couldn't believe what working people had to put up with. I couldn't understand why they weren't all raging communists. I worked in factories, petrol stations, offices, laundries, building sites. I remember living in a squat in London, my partner, myself and a very young child. I got to know the squatting community and people wanted me to become active in that particular area, and I have to say, even though I was involved in other forms of left-wing activism, I just ran away from it. It was so demoralising. I remember visiting one squat where a family were living with no electricity and the floor boards pulled up. It was heart of darkness stuff, and I ran away from it, back to the safety of other left-wing issues."

By the early '80s he was working as a presss officer for the UK-based Troops Out Movement, but then he returned to Dublin and got a job working for Hibernia, a long-running current affairs magazine that had been recently purchased by John Mulcahy.

"Hibernia had a policy of employing radicals," says Prendiville. "My boss, I suppose, regarded them as being more critical and inquisitive than other kinds of journalists. We had some mutual acquaintances and he took me on. Then John set up the Sunday Tribune with Hughie McLaughlin and when that went into liquidation, Vincent Browne picked it up with Tony Ryan, and I stayed with them. Then John started the Phoenix and when he asked would I come work there, I jumped at the chance." He smiles. "And I've been here 25 years."

At this point his radicalism took a back seat, although he admits that his republican activism had continued even as he wrote for the Sunday Tribune. "It was fraught," he says. "But I wouldn't have got away with it at, say, RTé. The
Tribune was a better environment."

Does he regret any of it now? "I don't. I regret that the radicalism has gone out of youth. When I was younger most of us were left-of-centre but that doesn't seem to be happening any more. I look at students now and wonder why they aren't more radical. It's all career, career, career, get the points, get a job. It individualises them. It atomises them. Maybe there'll be a swing in the other direction now. I came back to Ireland when Strumpet City was on – the book had been written a few years earlier. Jim Larkin and 1913 were so much part of the consciousness and the culture then." He sighs. "And then you look at how trade unionists are demonised today."

Does he think, as some of his critics do, that his politics colours his journalism? "I'm happy to admit my politics are to the left, but they get filtered out, because the story is the story. And we've got a very eclectic group of people writing for the Phoenix. Unlike most journalists who deny being politically prejudiced I'll admit to being left-of-centre and I'll admit to being reasonably republican. Any journalist who tells me they haven't got political prejudices is either a liar or an idiot."

One way or another, his background has fuelled 25 years of irreverent news-gathering. Who does he think reads the magazine? "I suppose we're read by the chattering classes," he says. "Politicians, campaigners, journalists, barristers – there are specific constituent groups who just love reading about one another. It's a very middle-class readership... with maybe some radical elements. It isn't too different to what the rest of the media does in that it's about hard news, but we have an irreverence and a style that's almost deliberately disrespectful. With the best will in the world there's a temptation for journalists to become part of the establishment. There are pundits who lacerate people every week but can't take the slightest pinprick themselves. I have a theory that something happens to people between the ages of 40 and 55 years of age where they start to adopt a different persona and begin to believe their own propaganda. Catching them in an act of hypocrisy is probably one of my greatest pleasures."

Any regrets? "Well, when we actually get something wrong we're made to regret it. Apart from that, there are very few stories I wish we hadn't run. I don't generally have regrets because we don't pick on the little people. Other papers do and I think that's unfair. Here at the Phoenix we pick on big people, and they should be big enough to take it."

Picking on the big people: The stories that made Paddy's day

The Reverend Hilliard's republicanism

"Church of Ireland rector Reverend Hilliard was an extremely popular man. When he was killed the Irish Times did a CV of his life and they mentioned everything except that he'd been a member of the republican movement. So we ran that story and the hounds of hell came down on us. We were brought to the high court for a criminal libel action by his widow with the massive support of the Irish Times. But they failed."

Charles Haughey and ben dunne

"We reported first on Haughey taking money from Ben Dunne," he says, before adding disappointedly, "but the rest of the media were quickly on top of that so we didn't get that much reaction."

Father Michael Cleary's son

"We broke the story that Father Michael Cleary had a son. The number of abusive calls I got after that really shook me up. But it was the early '90s and I think it was very significant in terms of the transition of Irish society out of clerical domination."

Mary Harney's transport arrangements

"She requisitioned a fishery protection aircraft to fly herself and her husband to Sligo. She sent the state car ahead of her to Sligo airport where she was collected and brought to Manorhamilton, Co Leitrim, to open an off-licence for a former boyfriend of hers."

Anglo Irish Bank 'technically bankrupt'

"Two years ago, before it became a pariah bank, Anglo Irish reported profits of €784m. In the same week we reported it was 'technically bankrupt'. As we were going to print we had this late-night legal confrontation with them because they wanted us to pull the article. We went with it anyway because we knew it was true."