Kate O’ Mara can scarcely conceal her disdain for her part in Murder On The Nile coming to the Oxford Playhouse on Monday.

Not only is her character quite detestable but she has to work twice as hard to add flesh to the bones.

“At least I play the part Betty Davis played, but I bet she had better lines,” she laughs in those famously sultry tones. “I play Miss Ffoliot-Ffoulkes who is a snob and bully of the first order. And when I first read the script I thought ‘this is appalling, there aren’t even any laughs in it’ because she is such a nightmare and has nothing to recommend her at all. She’s nothing but noise pollution all day long,” Kate says dramatically.

“But I have got used to her now and just go for it. So no, it’s not Oscar Wilde or Shakespeare, and Agatha is a challenge because the characters are very two-dimensional and it’s up to you to flesh them out and stop them becoming cardboard cutouts.” And, having just had her cataracts removed, this might be more of an effort than normal.

“When I first came out of hospital I thought ‘God Almighty it’s bright’” she laughs. “I can see everything now. And it’s very alarming. So I need to have a word with them about the lighting on stage. How will I manage?” she asks. She could wear shades? “Yes but the eyes are so important because they show all your emotions, and you need to see them flashing, so it’s going to be traumatic.”

Reading between the lines, although Kate is still an utter professional, this isn’t her favourite play in the world. “But that’s showbiz,” she replies, quick as a shot, “and a girl’s got to work. And anyway, good old Agatha,” she says mellowing a bit.

“Because although everyone’s seen it before, they still come back again and again because no one can ever remember who dun’ it which is terribly entertaining,” she says in that wonderfully growly voice, which has had men jibbering like idiots for decades.

Kate O’Mara came to prominence in the ’60s and ’70s in The Saint, The Persuaders, Champions and The Avengers, before hitting the US in the ’80s in Dynasty and returning to the UK in the ’90s for Howards Way and Ab Fab.

While her professional life has been a huge success, her personal life less so. “My relationships have all been completely unsuccessful,” she says honestly. “Because I like to be in control and men don’t like that. They want to run the show and be the tallest poppy in the field. And my friends say ‘Kate, what you need is a man to look after you’.

But that’s the last thing I want and I’m too old to change now. Because actresses always get attention and because I’ve always been reasonably successful...well, I’ve been independent for a long time now. “But I still get dressed up and go out as Kate O’ Mara — whoever she may be. I know what’s expected of me because if you have a reputation for being a tough girl, that’s what they want. And there’s no point being anyone else now, so that’s me. Although people who know me, know I’m an absolute pussycat,” she purrs. “I’ve just learned to get on with it, work hard, and I’ve got some wonderful friends and hopefully I’ll be able to leave my son something to be getting on with.”

As if reminded of her own mortality she then adds sadly: ”And Katherine, all my friends are dying. There have been so many this year and some are younger than me — Susannah York, Simon Ward — it’s been really shocking.” So her last tour then? She nods. “Yes, I find it all so exhausting. It’s not the acting, it’s the travelling and living out of a suitcase. But in between I come back here to my 16th-century cottage and it’s such bliss when I’m home.”

In the meantime there’s still 10 weeks of Agatha to get through.

She smiles: “While it’s not Cleopatra and I have to make a silk purse out of a sow’s ear, people still love it and are paying good money to come and see it. And obviously my prime concern is entertaining the audience. That’s why we do it, to hear them laughing, or on the edge of their seats, and it’s still enormously satisfying.

"So I take five minutes to centre myself, collect my thoughts, and concentrate on the part and on what I have to achieve. As I’m first on stage I see myself as the pace setter and being the leading lady is a real responsibility. I still give 150 per cent.”

Kate O’Mara appears in Agatha Christie’s Murder On The Nile from Monday. Box office on 01865 305305 or the website www.oxfordplayhouse.com