You play a safe cracker's wife in a new television drama. Ever had a brush with the law?

I had a battle with a gas company and I've had a lot of parking tickets; that's it. But it's so much easier to become a criminal now than it was.

Do you have a record?

No. But you make a noise at the wrong time or don't get your Travelcard out in time in London and that's it.

For a long time you were many men's pin-up; under pressure to look the part?

Yes, it's always been like that, but it has become more intense over the past few years.

Is a nip'n'tuck on the to-do list?

I'm too squeamish; I've got friends who have had facelifts and they look like they've been beaten up.

But the swelling goes down.

Yes, but their faces never settle down quite right. People always look like they've had surgery. If there were some pill or procedure that was painless and didn't leave the marks and scars I might consider it.

Ever worry about too many laughter lines?

I want to say that you earn the lines, but once in a while you can't help looking and saying, “Oh God.”

So you watch your weight and pile on the slap?

I do care what I look like, but I love food too much to be serious about watching my weight. I eat really well, though. I have fruit juices in the morning. All those red fruits are fantastic. I always think the more colourful your diet is, is the better it is.

Bit of a health nut?

I won't eat bread that tastes of cardboard, but I'll pick a nice whole-wheat loaf if I can.

Gym bunny too?

There comes a point when if you don't make yourself exercise you start to put on weight, so I swim three times a week and cycle and do the running machines at the gym.

Ever tempted to give the gym a miss and eat a bar of chocolate?

Dairy is my indulgence and I like real dark chocolate. I buy chocolate balls when we go to the Caribbean. They're pure cacao, with a little cocoa butter. You grate it and make a sort of tea out of it and you can add orange-peel and cloves. It's delicious.

Not such a bad vice; any bad habits?

I lack patience and it can cause horrible situations.

Such as?

Well, for example, I get cross when I'm driving with people in cars, then I realise that I know them. But it's when it affects the ones you love that it's hard. I can get really furious when things haven't gone my way. But I've never been a person who can pretend something's not happening. If I get cross, I get cross immediately, and it's upsetting for others but I can't stop it.

But you have a reputation for being such a nice person.

It can be a put-down “nice”.

So are you a bad girl?

I have imperfections like everyone else. I've met people who are genuinely really good, but I'm not like that. In a way if you're labelled “nice”, like I was after I did the film The Railway Children when I was 14, it can stifle you as an actress and as a person. You can't show your other side.

And did it hold you back?

Not too much. I joined the Royal Shakespeare Company when I was 28. That let me get away from the nice-girl badge. I played a murderess.

Green tea or your GP?

I use some alternative therapies as preventive measures, such as taking echinacea as soon as I feel a little rundown, and I think that massage can be therapeutic.

You're a supporter of the Cystic Fibrosis Trust. Do you have a personal experience?

My niece, who is 29, has cystic fibrosis. The lungs fill up with fibrous tissue, which traps fluid in them. It also affects the pancreas; you can't get the nutrients from your food. It's the most common life-threatening disease in this country. One person in 25 is a carrier and two people who are carriers can have a child with cystic fibrosis.

Are you a carrier?

I am.

Did you worry when you had your son, Jonathan, now 17?

I tested myself while I was pregnant, then my husband was tested and he wasn't a carrier.

What keeps you awake at night?

Unpicking things. Trying to justify things I feel I should have done or didn't do right. The fundamental doubts come out at night.

What are yours?

My mother died a couple of years ago. I find myself wondering if I did enough; did I spend enough time with her? She had rheumatoid arthritis. I always hoped for another good summer. I promised I'd be the diligent daughter. But the summer didn't come.

Planning on taking early retirement in the hope of catching all the good summers?

I put 65 on my forms but I won't stop working. I like the idea of retiring, picking up some paints or maybe getting involved on the other side of TV production. I don't want to see myself playing the part of an old lady in a retirement home. No way.

The Invisibles, BBC One, on Thursday, May 1, 9pm

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