UNTIL the other day I hadn't realised how seldom we see Amanda Burton smile on television. Interviewing her about her new BBC1 drama The Whistle-Blower, the conversation is punctuated with merriment of various degrees including a Burton rarity, laughter.

Perhaps she's so straight-faced on screen because of the roles, more dramatic than comedic. No one would expect her to do anything but suffer in a soap, so her four years as accountant Heather Haversham in Channel 4's Brookside were an emotional rollercoaster, low on fun.

The actress, whose faint Irish burr in her accent betrays her Derry upbringing, had to deliver endless bad news as Doctor Beth in medical series Peak Practice. And now as pathologist Sam Ryan in Silent Witness, she slaps internal organs on the scales like one of Dewhurst's top employees. There's little room for light-hearted banter among the corpses in the autopsy room. So, here we are at the BBC spring and summer launch in a ritzy London restaurant, and Burton is smiling - despite the procession of journalists plonking themselves down beside her to demand answers about her latest TV drama.

The amount of on-screen promotion of the two-parter going out over Easter shows the high esteem in which the Beeb holds Burton. She is one of their prime assets, a top telly name like David Jason and John Thaw who are automatic ratings winners no matter what they appear in.

Burton seems genuinely surprised by the fuss people, the public not just BBC hierarchy, make of her. "I sit on the bus going into town wondering why people are looking at me," she says. Clearly they are astounded to see one of TV's highest-paid performers travelling on public transport without a posse of minders and bag-carriers. They imagine stars - and Burton is an undoubted TV star - ride in big limousines and are cushioned from the harsh realities of life by bowing minions. But, as Burton will tell you, family always takes precedence over career. She and photographer husband Sven Arnstein have two daughters and they come first. When I suggest that she's managed to fit in having a family with having a successful career, she says: "They are my main priority. I don't fit my family in and about my work. Very definitely I fit work around my family."

The Whistle-Blower is a family drama of sorts. Burton plays a City banker who exposes a major drugs money laundering operation she's discovered. To protect themselves, she and her family - husband and two children - have to leave their home and friends and assume new identities.

It took a year between Burton being offered the thriller, by ER producer and writer Patrick Harbinson, and production beginning. "It was worth the wait," she says. "It was quite frustrating because I thought it was such a wonderful story that I could hardly wait to start shooting."

The role, she hopes, is something different. "She's a woman who does not know who she is. There's a basic unhappiness or not being very comfortable in everything - her work, her family, her love life," she explains.

"The whole beat of the film and the character is very, very different for me. She's very sleek, very sophisticated but almost like a round peg in a square hole. Just when you think you have a handle on her, she goes off on another tangent."

Burton does have a knack of choosing dramas and series that capture the public imagination. How she achieves that is simple. "You have always to have a huge amount of integrity in the projects you choose because you have to put yourself in the position of the viewer and ask yourself, 'would I want to sit down and watch this?'," she says.

"That's the main criteria, the way that you feel. For the amount of effort and money things cost to make, it has to be really good and worthwhile rather than just filling space. One hopes to achieve that, you have to feel it's going to be worthwhile, not worthy but worthwhile."

Inevitably, that means she turns down more offers than she accepts. "I would rather do less and make it good than a lot of stuff that doesn't have my full heart in it."

She does, of course, talk from a privileged position of a top telly name who has more power than most performers. But she points out: "My career has been a progression. I didn't come in with a great big bang."

Hard to believe but it was 19 years ago that she first appeared in Brookside when she didn't have a career so much as a life plan. She refuses to think in terms of when she made it, feeling it's not important to think along those lines.

She enjoyed filming the recent BBC wildlife documentary about bears and making more documentaries are an avenue she'd like to explore in the future. She's also looking forward to playing real life mountaineer and mother-of-two Alison Hargreaves, who died while climbing K2.

"I always love a challenge, pitting myself against something I know is going to be hard work," says Burton.

All very worthwhile but not, one suspects, a barrel of laughs.

* The Whistle-Blower is on BBC1 on Easter Saturday and Easter Sunday. Amanda Burton guests on Parkinson on BBC1 tomorrow at 9.05pm.