You're back in another strong female lead, as policewoman Clare Blake in the fifth series of The Commander. You also played Dr Sam Ryan in the cult BBC crime series Silent Witness. What attracts you to these roles?

I like characters who seem tough on the outside and have to hold it all together for professional reasons but who are as human as everybody else under the surface. Lynda La Plante (who writes The Commander) creates brilliant strong, female parts like Jane Tennison in Prime Suspect and Clare Blake too, but finds a way to deconstruct them.

Recognise anything of yourself in these characters?

Increasingly not. The older I get, the more accepting I become of myself and the less I find myself striving for perfection. I've realised that perfection doesn't exist and that if you constantly set yourself up to achieve it, you're riding for a fall. Of course, like most women, I still have those “does-my-bum-look-big-in-this” moments. But I feel that accepting your shortcomings makes you stronger.

You are looking particularly trim at the moment. What's your secret?

Running. When I hit the big 5-0 two years ago, I decided I needed to face it by doing something positive. I started training for the Great North Run and discovered that I loved it. I can feel the endorphins kicking in. It's a complete happiness boost. Last month I ran again in the same race, although work commitments meant that I couldn't do a great deal of training. But fortunately, I think I now have a general level of fitness that's pretty good and the rest I make up for with determination.

What about your diet?

I try to eat organic, seasonal produce and I make a lot of juice from fresh fruit and vegetables because, for me, that's the best way to give my system a huge boost. I'm eating lots of autumn produce, cabbage, greens and root vegetables, at the moment.

Does it keep you young?

I'm not especially worried about getting older. I have huge amounts of respect for the older women I meet who are fantastically philosophical and believe, as I do, that the more you obsess about it, the bigger the headache you create for yourself.

You're looking rather happy in general. Is it true that you're in a new relationship with the photographer Stephen Colover?

Yes. I'm very much in love and it's rather gorgeous. It's like having a light inside. Falling in love is totally different at this age because you're with someone because you want to be with him or her and for no other reason. You aren't going to produce children and that changes everything.

Speaking of children, what's your relationship like with your girls?

Even though my daughters [Phoebe, 19, and Brid, 17, from Amanda's marriage to the photographer Sven Arnstein] are more or less grown up, they know they can talk to me about anything, which I really love and yet I don't intrude on their life. There will be some readjustment when it's time for them to fly the nest because motherhood has been the biggest job of my life. But the cycle turns and now it's their time to go off.

You grew up in a Protestant family in Northern Ireland. Was religion a big part of that?

Yes, I still like to go to church to hear choral singing or just to sit quietly and think. I love Christmas and find the whole period leading up to it a very spiritual time, maybe because it's all about birth and renewal.

Your father, Arthur Burton, was head of a village school in Ballougry, Co Derry. Ever thought of following in his footsteps?

Yes, my father was totally inspirational. Two of my three elder sisters became teachers mainly because of his influence. If I hadn't had a burning desire to act, I probably would have done the same. But I think he understood that acting was something I had to try and I'm glad that both my parents, who have passed away, lived long enough to see me make a living out of it.

Green tea or GP?

I'm definitely a bit of an arnica and lavender oil girl. I love reflexology and am a sucker for an aromatherapy massage. I have them as regularly as I can. That's not to downplay conventional medicine. Sometimes a Lemsip and a hot-water bottle can be very handy too. Nurofen is the saviour of all long-distance runners.

Any plans to marry and give us a happy ending?

Not at the moment, although I've read that I'm “engaged”. I don't know about an ending; it's more of a beginning. I find myself at the happiest possible point at the beginning of my fifties. It's a rather wonderful feeling.

INTERVIEW: DAPHNE LOCKYER

The Commander, ITV1, November 10, 11, 12

Explore Women

• Fashion

• Beauty

• Diet & Fitness

• Relationships

• Families

• Celebrity

• The Way We Live

• Horoscopes

Times recommends

• Live chat: Thrifty ways to update your winter wardrobe
• Is anybody out there really listening?
• Nutrition Q&A: Will eating late make me fat?