The dark, back office of a Georgian house in Bloomsbury is an incongruous place to be interviewing Ellen Pompeo. But that's where The Telegraph (U.K.) tracked her down for the second of two exceptional interviews we've found featuring the Grey's Anatomy star this week.

Yes, it's a far cry from the sun-baked Los Angeles lot where Pompeo is usually to be found, in scrubs, as the title character in Grey's Anatomy.

Dr. Meredith Grey - brisk, vulnerable, self-destructive, talented - is a lead unlike any other on American television, and her gripping screen presence and romantic train wrecks hook 20 million viewers a week.

In its annual "Celebrity 100" power list, Forbes ranked Pompeo and her co-stars number 12, while the Desperate Housewives cast fell to 47.

Yet in Britain, where the drama is the main draw on the digital channel Living with reruns on Five, Ellen Pompeo is hardly a household name.

Male critics have sniffed at the 'vapid' scripts and 'mawkish' acting in the drama about five trainee surgeons at a Seattle hospital.

But Ellen Pompeo's portrayal of a woman totally competent in her work and an utter disaster in her relationships has forced even veteran Hollywood producers to examine how a lead wh's such a mess - prone to getting drunk in bars and picking up strangers - can prove so compelling.

The tabloids have focused on Pompeo's weight (she's supposedly anorexic), behavior on set (she's supposedly a diva) and, since her November engagement, the colorful past of her fiancé Chris Ivery, a record producer, and the size of the engagement ring he gave her.

This, a dazzling oblong diamond, has caused Ellen Pompeo so much angst that she is even now twisting it off her tiny hand.

'Completely garish, isn't it?' she asks. 'He got it in Beverly Hills and spent his entire life savings, which I could kill him for. I was very mad about it. Some days I really love it, and some days I just want to sell it and give the money to charity. All the magazines care about is the size. I think, "Oh, it's absolute rubbish and I'd like to throw the ring in the sewer."'

Continue reading The Telegraph's lengthy, revealing interview with Ellen Pompeo after the jump ...

She looks at me wryly.

'I know! How fortunate of me to sit here with this giant rock when there are babies in Africa fighting for their lives.' She has gone from making no money to making great money. How does that feel? 'I feel guilty.' She gives a high, truthful laugh of embarrassment. 'I feel guilty!'

Like so many Hollywood stars, Pompeo is small and fragile. Her hand, when I shake it, is like a bunch of twigs and her muscled arms are as tiny as a child's.

She is wearing a black sleeveless cotton dress over thin black leggings and Lanvin ballet flats, and in person looks completely different from on screen - younger and more innocent, a cross between Michelle Pfeiffer and Calista Flockhart.

Her long hair is healthy and red, her blue eyes have a tinge of green and she keeps almost constant eye contact in a way that is not at all uncomfortable.

Here on her an eight-week hiatus from Grey's Anatomy, she and Ivery are looking for a London flat to buy, before zipping on to Paris and Tokyo.

You feel that it is only now, at 37, that Pompeo's life is starting to make sense - Ivery's too, perhaps, following his three jail sentences, two for drug convictions, before they met. He now works scouting talent for the music producer Randy Jackson from American Idol.

Pompeo, meanwhile, is on her fourth season at Grey's Anatomy, of which she is the undoubted star (with great support from Patrick Dempsey and Sandra Oh from the film Sideways).

The drama has gathered Emmys and Golden Globes since it debuted on ABC in March 2005. Pompeo is paid $200,000 an episode, and her story seems to be a Cinderella tale of late success, even including a mother's death and a tricky stepmother.

She had a sad, difficult childhood as the last of six - she was eight years younger than her nearest sibling - in the blue-collar town of Everett, near Boston, and was four when her mother, Kathleen, died of an overdose of painkillers. Her first memory is of her siblings attempting to revive her.

The trauma in this vignette is hair-raising, and she admits, putting her hand to her throat, 'I had a tragedy as a child, obviously, my mother dying, and it sort of… I suppose I describe it as… it sort of left me with a broken heart.' But can you mend a broken heart? 'No, never completely.' Her voice lifts, childishly. 'But that's OK, because it makes me appreciate my life.' Had she found therapy useful with that? 'No, I think my job is therapeutic.

It was quite a tragic thing, all these children having no mother; it was quite difficult on my father,' she continues.

'And then he remarried shortly after my mother died, and, ah, much too soon. It was… quite a bad situation for all the children.' Why, what was her stepmother like? 'Oh, I'd rather not discuss that. So I would go off and stay with various people. I was always being shuffled around. Who could baby-sit me this time? So I would go for the summers and the weekends to my aunt Ellen, who I'm named after, and my uncle Jimmy on the Upper East Side of New York. My uncle Jimmy took me to the theatre. And another of my mother's sisters, Sister Maureen, was a nun and lived in a convent in the Bronx, and I would go stay there often, as well.'

Pompeo says, batting away sympathy, that those 'different experiences' gave her a lot to draw on in her acting. But she also concedes that, 'I was just completely confused. I knew I had a lot of people who loved me.

There were a lot of different types of people in my life, and I had all these brothers and sisters who were crazy hippy teenagers, smoking pot in the wild 1970s - rock 'n' roll - and I had my dear, dear grandparents…' Everyone, but no one? She pauses. 'I did… well, you know, I had everybody but the one person I really wanted.'

Her father, Joseph, a tobacco salesman, was a strong character. 'He intimidated everybody. He'd wait at the window and when they dropped me off in front of the house he'd fly out of the door and rip them out of the car by the neck,' she has said, alarmingly, of her teenage dates, but he also told her she could do anything she wanted in life.

What she wanted was to act. So the moment she turned 19 she made for Miami, where she got a job as a cocktail waitress.

Despite her fragile, feminine appearance, she was no pushover. 'I'd abuse the customers, yell and scream at them and make them wait. If they put money down on the bar and it wasn't enough, I'd go wait on someone else. Pretty soon there would be $20 on the bar,' she once told Playboy. I love that image of you at the bar, I tell her. 'Right!' She laughs with real amusement. 'Well, I don't know if you've seen The Departed, but Boston, my home town, is a corrupt place. I grew up in an Italian-Irish neighborhood, and there were Irish gangsters and Italian gangsters. It's very much like a modern-day Gangs of New York.'

After two years in Miami she went to New York. But her dream of becoming an actress still seemed 'such a grand thing. I felt so overwhelmed, you know, "How do I figure out how to go about this?"' She was also suffering profoundly from her childhood. 'It's as if the floor beneath you is… as if a board is always going to fall through.'

She was 25 when she got her first break; an acting agent approached her as she was working the bar at the SoHo Kitchen. The agent put Pompeo up for three adverts; she got all three. Then Pompeo landed a part opposite Jake Gyllenhaal in the 2002 film Moonlight Mile.

He, by chance, had come up to her in a car park three weeks previously and told her she was 'the most beautiful girl I've ever seen in my entire life'. For her the coincidence was life-changing. 'It sort of hit me that I was being guided,' she says. 'I had sort of spent my twenties up until then looking for some sign of my mother, you know, "Make the chandelier swing and show me that you're with me." And at that point I put my faith in the idea that life gives you signs and, whether it's my mother's spirit or not, I've had too many coincidences in my life for it to be normal.'

Another was the way she met Ivery. They had grown up two miles apart but met only in 2003 when a mutual friend introduced them at a Whole Foods shop in Los Angeles. 'I knew his background and I knew the circle in which he ran and I didn't want anything to do with it,' she admits. 'You think you want to get away from your past and be this completely different person. And then I run into him again two days later and by this time in my life I know that's no accident. I knew he was supposed to be in my life.' He had gone to jail briefly? 'Oh, yes, a couple of times. But most people I knew in Boston did. It was very common, which is why I had to get out.'

Something of Pompeo's childhood vulnerability comes off the pages of her previous interviews and you hope, before you meet her, that Ivery is good news. He drives her to work and visits the set most days; she says they do everything together. 'To know someone - the real them, not the reinvented Hollywood them, with all of their flaws and all of their past - that's a true relationship,' she says. 'I feel very lucky. It's very solid.'

I ask what she makes of her character's romantic travails in Grey's Anatomy.

'She has a complete lack of emotional intelligence,' she exclaims. 'I just want to smack some sense into her.' What would she advise her? 'Don't ever beg a man.' (She is referring to the scene where Meredith pleads with her married lover Derek to choose her.) 'He should be begging you!'

So what's next for Ellen Pompeo?

Halfway through a six-year lock-in for Grey's Anatomy, she and Ivery are now trying for children. Does their forthcoming wedding excite her?

'No, I'm not someone to stand on ceremony. That's why I have such a problem with the ring. It is a symbol. Just rather an extravagant one.' She gives another high laugh of embarrassment.

I say it must feel like it's all coming right. She smiles. 'I think so. A friend who I moved to Miami with when I was 16 or 17, he was photographing me back then and said, "You're going to make a great 40-year-old." I didn't know how to take that at 16 or 17, but I never forgot it. Now I feel like the older I get the more I am able to take on.'

Her publicist is mouthing that we have to finish. 'I love the architecture round here,' Pompeo says, getting up.

'It reminds me of my home town.' I catch sight of her in the next room as I leave. She looks different now, 17 again, a sprite, a slip of a thing, in her teenage black wardrobe.

'I took a sleeping pill last night, which I don't usually do, because my body is too little to take it, and this morning I was all over the place,' she exclaims. 'I could hardly manage to dress!'

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.