Uncharacteristically Sinead

SINEAD Cusack is adamant that she is nothing like Hannah Thornton: "When I was asked to play Hannah I couldn't believe it," she avows, with genuine astonishment.

"The first question I asked was Why'? You know, you have this image of yourself and I think I'm a jolly Irish woman; I sing a lot and laugh a lot and generally am quite sunny. I never thought of myself as dour, but obviously the casting people thought I was the right person, so I've got to re-evaluate now how I come across," she adds with a laugh.

And it is very difficult to find any sort of resemblance between the charming, humorous Irish-woman, with a thespian pedigree and a reputation as one of the UK's foremost classical actresses, and the forthright northern industrial matriarch that she plays on screen in BBC One's North and South.

Sinead goes on to admit that taking on the role of Hannah did not come easily.

"I thought, this is a difficult one for me, a bit of a departure. I've played the northerner before, but not often, and I've played powerful and tough women before, but never anyone quite like Hannah."

However, Sinead is clear that it was putting on the costume that really helped her to get into character.

"When I was in costume fitting for the first time I looked in the mirror and was horrified by what I saw: this dour matronly figure dressed top to toe in black bombazine."

Cusack plays the matriarch of the Thornton dynasty; a woman of formidable character, who broaches no nonsense to run a cotton mill in the industrial northern town of Milton with her son, John (Richard Armitage).

"The thing that defines her most is her co-ownership of the mill and her relationship with her son," she explains, "which is incredibly close But the nature of the woman is that her emotions are always extremely reined in. As far as Hannah is concerned, the passion that she feels for the mill, for her son and her way of life is crucial to her DNA."

But Hannah's affection for her son is poles apart from her relationship with the household's only daughter, Fanny (Jo Joyner).

"Her relationship with her daughter is lacking," outlines Cusack. "I wondered whether Fanny in some way reminds her of the husband that let her down and almost caused the ruination of the family. It's not good. It's almost like a tolerance rather than an understanding. I think she's embarrassed by Fanny because she is frivolous and her values are completely alien to Hannah's and John's. Her values are to do with the exterior, the superficial whereas with John and Hannah it's hard graft and just and fair and being committed all of those northern values that define northern peoplethat's a side to Hannah that doesn't reflect well on her."

Ask Sinead whether she thinks audiences will come to like Hannah, and she pulls no punches: "I don't think Hannah's easy to love. Richard loves her, but he's the only person who does. I think she's frightening, she's judgemental and she's tough. But she is fair. Her relationship with Margaret is determined by her love for her sonI hope people will see that at the base of her character."

Sinead comes from a theatrical dynasty. Her family goes back three generations of thespians grandparents, parents and two sisters Sorcha who was in Casualty, Niamh known for her role in Heartbeat and Catherine who has been in the top soap Coronation Street.

Sinead admits that at an early age she didn't really want to follow in the footsteps of her family.

On the contrary, she chuckles, she had more lofty aspirations at an early age: "I wanted to be a saint and in my teens wanted to be a nun. I then passed on from that and wanted to be an academic or a journalist before finally realising the only thing I can really do is entertain people."

It was only when she got older that Sinead realised she couldn't escape from her heritage, although her acting and academic career may have been cut short abruptly following one particularly raunchy performance while at school.

"I remember one piece I wrote which was about the Profumo affair. We did it as a review sketch for our teachers, all of whom were nuns. We had one paper that we used to get, but the nuns would cut out all the titillating pieces so that my grasp of the Profumo affair was tenuous in the extreme. I played Christine Keeler and I was nearly expelled from school for it."

After an undergraduate career reading English, during which time Sinead also trained at the Abbey Theatre in Ireland, Sinead's first screen break came when she was 23, playing opposite Peter Sellers in the 1970 film, Hoffman.

Since then she has become a major name in film, TV and particularly the theatre, where she has won awards, particularly for her outstanding performance in Our Lady of Sligo. Nobody, however, is more surprised at her continued success than the actress herself: "It's amazing to me that I'm still at it," she avows.

"I made every possible mistake one could make as an actor. When I should have been using my youth and energy and unlined face to promote my screen career I was busy trying to get in to the Royal Shakespeare Company to do classical theatre. Once I got in there I hung on with my fingernails. I had done some film and TV in my 20s, but I spent an awfully long time in the theatre when I should have been out there making my face my fortune. But I didn't. Then in my 40s I came out and thought I should do some telly and film and some things came along and I'm still at it. I do love variety, though, hopping from one medium to the next."

When Sinead is not working, she likes to spend time with the family at their home near Watlington with husband Jeremy Irons and their two sons, Sam,26, a photographer, and Max,18, himself an aspiring actor.

Her face lights up when she talks about the lads'; and although they are both independent souls, she is adamant that she'll be there to look after them and protect them if needs be: "I'm happy with whatever my boys want to do. I'm passionate about my lads. I'm passionate that they're happy with whatever they chose to do. Both their chosen professions are extraordinarily tough and full of rejection and you just pray that they will survive all that."

In this respect, at least, Sinead Cusack doesn't seem so different from Hannah Thornton after all.

North and South is on BBC One on Sunday at 9pm