Some things are off limits for Des Keogh and Rosaleen Linehan's new show, but politics isn't one of them, they tell Arminta Wallace

The boardroom of the Gaiety Theatre is a modest space. But it could tell a million stories. "Look!" says Rosaleen Linehan as we settle ourselves at the table. She points through the open window to the other side of the building. "That's dressing-room number two, over there." Returning to that particular dressing-room one night during the interval of a play, Linehan put her key in the door. It wouldn't open.

"They broke down the door - and sure enough, the room had been broken into and a small amount of money and some other stuff taken. After a lot of head-scratching, they found footsteps leading out of the loo just up the corridor there, and across the roof. They asked the young fella selling ice-cream had he seen anybody acting suspiciously and he said yes, he had - and when they took him out into the auditorium, he spotted the chap sitting in a box, cool as you like. It was the last night of The Plough and the Stars. The police were sent for, and as we were taking the final bow, Donal McCann - in mid-bow - hissed at me out of the side of his mouth, 'they've got yer man'. He had done the deed, come back into the theatre, bought a big round at the bar during the interval, then stayed to watch the end of the show. It's like Alfred Hitchcock, isn't it?"

And they're off, batting memories back and forth like tennis balls. Keogh, it turns out, has another Gaiety boardroom story. "We were doing a sketch where I was the interviewer and Rosaleen was playing Garret FitzGerald - who was Taoiseach at the time - and who had had a sex change."

"Tootsie Garret," says Linehan quietly.

"And Garret and Joan," continues Keogh, "came to see the show. Well, afterwards they were here - in this room - and we were asked to come up and say hello to them; which, of course, we were delighted to do. So we were chatting away, and finally they said it was time to go. And they left; but Joan left her handbag behind. About 30 seconds later, Garret flounced back in and said, 'I forgot my handbag, dear'."

We all look at the door as if the former taoiseach might still be there.

At this stage, Keogh and Linehan could almost measure out their comedy career in ex-taoisigh. They've been appearing together in musical revue since . . . well, since when? The early 1970s, wasn't it? Umm, they say. Hmm. Yes. A long time.

"It's 20 years exactly since we appeared on the Gaiety stage together," offers Keogh. "That was for Two Faced, in 1985. Then we didn't do any shows for 15 years, until Des and Rosie Ride Again, in 2000. Last year we did Des and Rosie on the Loose at the Pavilion in Dún Laoghaire."

And here they are, rehearsing Des and Rosie on - inevitably - the Luas. Funny thing, comedy. When you examine it too closely, it tends not to work. But there's no getting over the fact that 30-odd years is a long, long time in the comedy business.

When Keogh and Linehan began doing these revues, alternative comedy hadn't made it to the planet, let alone the mainstream. They were reared on laughter of the Noel Coward/Kenneth Williams kind; and their show is still a fast-moving combination of musical numbers, sketches and political satire. An alternative to the alternative, you might say?

"Well, we did use the F-word last year, you know," says Linehan proudly. "Once."

"Just for effect," puts in Keogh.

"There isn't," he adds, "a huge sexual content in our show."

Linehan gasps. "Huh," she huffs, smoothing her hair. "You speak for yourself."

Their timing is impeccable, each answering the other in an apparently effortless exchange which is, in truth, the result of years of rehearsal and performance.

Keogh admits they were nervous about returning to the comedy fray after a 15-year absence; but the Pavilion was packed for last year's run, hence the move to a bigger theatre this summer. How do they account for their continuing appeal?

"The tailoring of comedy is different nowadays," says Linehan. "But the process is exactly the same. You still build it up; you're still trying to make people laugh."

Keogh is shaking his head - but for once, he's serious.

"I don't quite agree with you," he says. "I think we differ greatly from the alternative people because I think we deal with more public subjects - social comment, stories that are in the newspapers. They seem to deal with private things. Going to the toilet and stuff like that."

"Well, yes," says Linehan. "I know one young gentleman who went along to one particularly alternative show, and reported afterwards that 'you can only take so much of periods and underarm hair'. But what I was really saying is that although it's different subject matter, the actual structure of the joke is the same. Maureen Potter used to say there are five jokes - in the whole of eternity."

Right on cue, we all laugh. But then, as their fans know only too well, this pair could make a ham sandwich seem side-splittingly funny.

"We've always had huge audiences, thank God," says Keogh. "And though the rehearsals are really hard work, when you get out there and the audience is reacting to you, it's fabulous."

"Ah, there's nothing in the world like it," says Linehan. "And when it really gets going, there's a nice kind of party feel to it - the audience seems to have, almost, a personal input into the whole thing."

Is that thanks to the local nature of the subject matter? "Yes," she says. "And there is no way this show could travel. It can barely go to Cork - do you know what I mean? It's specific. And its shelf life is nil; which is very sad, from the point of view of all the hard work that goes into it. But this is it. This three weeks is it."

Keogh grins. "I remember in - '89, was it?" he says. "We put on the show in the Gate, and they brought over somebody from the Edinburgh Festival. It was arranged that we'd go for a meal with them after they saw us go through our paces. And there was just a deafening silence. All through the meal, they never mentioned the show at all."

More laughter. "That was funny," says Linehan. "No, we don't travel at all."

Not with this show, perhaps: but both Keogh and Linehan have, as usual, been busy over the past 12 months. Linehan has just finished a run of Lorca's Blood Wedding at the Almeida in London with a cast which included Gael Garcia Bernal, star of the Oscar-nominated movie The Motorcycle Diaries, and a musical version of Joyce's The Dead in Pittsburgh. The former attracted rave reviews and was packed every night. Was the latter a horror, or a delight?

"It was both," she says. "It was a bit clunky at times, as if it had got stuck at the workshopping stage, but of course you can't go wrong with that fantastic last scene. And the score is absolutely beautiful because it uses the type of songs of the time. The musical director was fantastic. I learned things - at this stage of my life, imagine - that I never would even have dreamt of.

"When I got the script I gave it to Fergus [her husband] to read, as I always do. And he started to laugh. I said: 'What's wrong?' He said: 'Your character is described as frail. Do you think you can manage frail?' I said: 'At a push, I suppose I could.' As it happened, the other two women in the cast were fine, big, buxom women - so I actually did manage to look quite frail compared to them."

Keogh, meanwhile, has been touring his one-man John B Keane adaptation, The Love-Hungry Farmer, to great critical and popular acclaim, both in Ireland and further afield. "I'm taking it to Adelaide in February," he says, "and there may be a chance of a run in London as well. John B Keane is very big. Prior to that I did The Matchmaker, which was also very successful. Odd, you know, since I'd never done any of his stuff before."

Back at the comedy front, if comedy in general has changed, does that mean anything goes? Or are certain subjects still taboo? "Well, oddly enough," says Linehan, "last year we had one number about obesity. I triedit on three different nights, and was nearly frozen off the stage.There are strange areas where you can't go - where people don't want you to go."

Keogh nods. "And there are plenty of things that are just not funny. We wouldn't joke about paedophiles, for instance."

People's private lives and families are also off-limits, a civilised dictum which applies - it seems - even to politicians, although the current crop can expect some pretty merciless ribbing over the next three weeks. Gerry Adams, for instance, will appear "in person" for the first time.

"I'm trying to think," Linehan says, "whether any politicans actually come to the show nowadays. We used to have a huge following of politicos. Jack Lynch, for a start. Brian Lenihan was a great theatre-goer. So was Richie Ryan."

Keogh is chuckling again.

"Do you remember," he says, "when Charlie was up against George Colley, and you said: 'Isn't it terrible to think we have to choose between a crook and an eejit?' "

Laughter - then silence. Nobody can think of an answer to that one.

Des and Rosie on the Luas opens at the Gaiety Theatre, Dublin, on Sept 5 for a three-week run