ROUGH DIAMOND has the ingredients necessary to make it a hit. A beautifully shot drama with satisfyingly messy interpersonal relationships, with an idyllic Irish countryside backdrop and a Sunday evening slot on BBC1 - so far, so very Ballykissangel.

Conor Mullen, meanwhile, the 46-year-old actor who plays horse trainer Aidan Doherty in the series, ticks all the right boxes when it comes to leading-man material. He has the prerequisite good looks; the mellifluous voice (you may or not register it as being the voice of eircom's answering service) and that intangible quality that makes him capable of lighting up a screen.

Plus, he's got the lineage in the form of a rather famous drummer cousin, U2's Larry Mullen, although he says the latter hasn't impacted on his career in anyway, except for a couple of cheesy headings on press interviews.

Yet while he's been a well known and liked actor for over two decades, both here and in the UK, he hasn't achieved household name status to date. Rough Diamond, however, is guaranteed to raise his currency considerably. Is he ready for it?

"It would be great. Overnight success after 20 years and all that stuff!" he quips.

But no, he doesn't think that however well Rough Diamond does, that it will change his life dramatically. "I think it would be more difficult if you were younger and you were just out of drama college and you weren't knocking around for years, " he says.

"People that I know and friends of mine aren't too impressed by the fact that I'm an actor. I'd be surprised [if his life changed].

But I haven't been here before so maybe I'm being naïve?" In his role as Doherty, Mullen plays a charming, talented and unreliable ladies' man, who has overcome a gambling problem but hasn't addressed the other problematic areas of his life, specifically his dire financial straits and a stable with no horses. Charlie Carrick (Stanley Townsend) is the millionaire owner of a neighbouring yard who is keen to buy up Doherty's land and expand his equine empire, while Yolanda, Carrick's wife, played by Lorraine Pilkington, is the vet and former teenage girlfriend of Doherty, and there's obviously unfinished business for both. Throw in Jonah (Ben Davies), the teenage son Doherty never knew he'd fathered after a fling with a Newmarket waitress, who turns up unannounced one day at the yard, and the scene is set for all manner of intrigues.

Mullen thought from the outset that it had great potential. "I hadn't really heard that much about it and then the script was sent to me and I thought, 'This could be good, this could be something really exciting.' I read it and it was one of those things where I went, 'I could do that', so I took it very seriously from the word go; I thought I could give it a lash."

He can see how comparisons might be drawn with Ballykissangel but thinks that Rough Diamond, as a faithful depiction of modern Ireland, is edgier. "Charlie Carrick is Celtic Tiger. It's not that he's soulless but the way he operates, he's working off databases and spread sheets. It's not very organic and it's obviously money driven and it's quite flash. Then you've got Aidan's yard which is much more organic and supposedly magical. On the outside it's broken down but there's something really special and different going on there, in the way that they deal with horses and I think maybe there is a parallel that you can make about where we are now and where we were 30 years ago, " he says.

It was a pleasant working environment, made particularly so by the fact that he'd worked with Townsend before, had been directed by Eamon Morrissey (playing Dermot, the sage old groom) in the Abbey and knew Pilkington from seeing her around studios. Mullen was also grateful that he was confident around horses.

"It was only when we started really that we realised how important that was, " he says. "It's not just the riding. You're filming in a tiny little stable; the camera is there and the horse is there. You've got to be able to bump them and nudge them around and move them and move around them without being nervous." The horses' presence actually added an element of spontaneity to filming. "It kind of freed up a lot of scenes.

You're having the relationship with a horse while you're trying to play a scene and have a relationship with someone else, and the horse might take a nip out of you while you're doing that and you kind of have to incorporate that into what you're doing. It was good."

Prior to acting, Mullen started out in sales and ended up working for his father selling medical and surgical supplies for a couple of years. It didn't work out because it was a highly specialised field and he wasn't qualified. At this point, he was 22 and started going to plays, before joining the Brennan Smith Academy and inevitably developing the acting bug. He went to New York and stayed there for two years and then returned to Dublin. "There was nothing else I could really do and it looked good on the CV - actor in New York, studied acting for two years, so I started getting work and that was that, " he remembers.

The life of an actor, he concedes is not an easy one. "It is hard, even if things go well for you. I've been pretty fortunate and I'd still say it's a hard life. You're constantly being judged. People can be merciless." He recalls doing a play in the Peacock, which got two very different reviews. One of them mentioned his performance as the highlight of the evening. The other review opined that it was a fantastic night except for the lousy performance of Conor Mullen.

"You go, feck it, what's what really? All you can do is your best and if there is a grain of truth in your criticism you just try and amend it the next time you do something."

He says he's his own worst critic anyway, but that "you've got to leave yourself alone.

There are enough people out there who will judge you harshly."

Rough Diamond is already opening up new doors for him, giving him the freedom to be slightly more choosy about jobs, something he says is a relatively new experience for him.

"I try to be [selective] but you know, ask any actor. One day I'm going, 'Well, I don't do shit', and then suddenly the ESB bill comes in and you're sticking on the clown outfit. Now I'm kind of lucky in that I can be sort of selective. Not necessarily literally, as in, 'Oh, I'll do this or I'll do that', but I can be selective in what I put myself forward for and whether I get it or not is another thing. I think you've got to keep pushing the bar. If you don't, I don't think you - well again, just for me - you don't learn as much. Like everything, I think you need to keep going forward."

When he is between jobs and not doing voiceover work ("to keep the wolf from the door") he confesses to being lazy by nature and not really doing a whole lot. Home is Howth, Co Dublin, where he lives with his partner, the actress Fiona Bell, who he met on the set of Soldier Soldier in 1991. They tackle their work in different ways. "She's very rigorous and her approach is very methodical. I'd be more of a. . . I don't know, wear it out for a while and see how it fits, " he thinks. "It's interesting because I've certainly learnt a lot from the way she approaches things and benefited a lot from her opinions or her criticisms. It's good to have someone there who knows what they're talking about but like I said earlier on, it can be pretty rough if it's a criticism."

His two daughters from a previous relationship, Hannah and Georgia, have both expressed a desire to follow him into acting, elder daughter Hannah especially. "I was doing another interview and somebody asked me if I pushed them and I said I don't push them one way or the other, and Hannah read it and laughed and said, 'You are always trying to get me out of it and telling me to go do something else.' But the rejection is hard.

You get more 'nos' than 'yeses'? 'We don't like you', 'We don't think you're good enough?'" However tough he thinks the business is, for women he thinks it's a lot harder. "For a start, in any given selection of plays or films or TV scripts, there are more male characters than there are female characters, " he explains. "There are also more actresses than there are actors so taking that into account, it's probably twice as hard for actresses. And, they also have the pressure to be young and beautiful. But it's getting the same for men now."

'Rough Diamond', RTE 1, Fridays at 7pm and Sundays at 4.15pm; BBC 1, Sundays at 8pm