Fifteen minutes into my tête-à-tête with Rachael Stirling, I am suddenly struck by her physical likeness to a young Diana Rigg at the height of her mid-1960s Emma Peel fame. Yes, I know, the fact that Rigg is Stirling's mother makes the resemblance unsurprising, but the facsimile remains disorientatingly flawless.
"It's those brown eyes, babe," says the actress when I mention it, but in fact it's the whole face.
Enough of the miracle of genetics, though, for now we must discuss London property prices.
Capital is BBC1's new three-part adaptation of John Lanchester's 2012 state-of-the-nation novel set on a single gentrified street in south London, where the varied residents are being insidiously menaced by anonymous postcards declaring: "We Want What You Have."
Stirling plays Arabella Yount, the shopaholic wife of investment banker Roger (played by Toby Jones), whose pampered world starts unravelling when Roger doesn't receive the annual bonus he had been expecting. Arabella has some of the best lines, but the character must have been hard for Stirling to like.
"It's interesting that people point the finger at her for being the materialistic one, not Roger," says Stirling.
"It's interesting that it's the woman who's villainised, yet the reason she's transfixed on tarting up the house is a total lack of affection from Roger. Her redeeming feature is that she loves him. She also makes me laugh and I always like a character who makes me laugh.
Stirling was born and raised in London, only vaguely aware of her mother's celebrity status - and of the way that fathers at her Earls Court primary school would look at "ma", as she calls her.
Holidays were spent in Scotland, at the family home of her father, millionaire businessman and theatrical producer Archie Stirling, an arrangement that continued after her parents divorced in 1990 following her dad's affair with Joely Richardson. Stirling was 12 at the time, and had just arrived at an all-girls boarding school in Buckinghamshire.
"I don't have any self-pity about it," she says. "It was only traumatic as it was in the papers and the housemistress insisted on buying the Daily Mail - which invariably had a story in it about my parents separating."
Her ma and pa remain friends, and Stirling will, as usual, be visiting her father's baronial pile in Ochtertyre for Christmas, along with her mother and stepmother Sharon, who are apparently now great friends. In fact, Stirling comes close to recommending divorce as a form of personal development.
"Some people ask, 'would you like them to be together?' and I wouldn't because I now have two great relationships," she says.
Stirling went on to Edinburgh University to study Russian, while simultaneously starting her acting career in 1996 with the National Youth Theatre. She had to miss her graduation ceremony because she was busy making her first film, 1998's Still Crazy, a comedy about a reformed 1970s rock band starring Bill Nighy and Billy Connolly.
The fact that she was Game of Thrones star Diana's daughter brought with it certain assumptions, such as that she knew what she was doing in front of camera.
"They told me to hit my mark and I hadn't a clue what they were talking about. It took me 12 takes to walk through a door and by the time I finally got it, Billy Connolly was clapping very sarcastically."
In 2002 she played Nan Astley in the BBC's explicit adaptation of Sarah Waters' historical lesbian novel Tipping the Velvet. The drama made Stirling's name, but also, she says, made it hard for casting directors to take her seriously.
"I was offered every lesbian part under the sun and every opportunity to take my clothes off. I was quite naive. I should've known better, but I didn't comprehend where I was at."
The intervening years have seen Stirling steadily develop as an actor, with TV roles - including Ursula Brangwen in a 2011 adaptation of Women in Love, as Millie in ITV's wartime costume drama The Bletchley Circle - and some particularly fine stage performances, including two Laurence Olivier Award nominations in consecutive years (for The Priory at the Royal Court and An Ideal Husband at the Vaudeville).
The nominations coincided with the end of a five-year engagement to fellow actor Oliver Chris, prompting a decision to go and work in a pub in central London.
She says: "I'd done a runner from a boy I was supposed to get married to, and he was an actor, and I was being offered really mediocre scripts and I was a bit of a mess.
"People would come in to the pub and say, 'have I seen you on the telly?' and I would say, 'no you're probably thinking of Martine McCutcheon.'"
Stirling's five-month career break appears to have worked. She has she had one of her most rewarding years to date, playing Mackenzie Crook's girlfriend in the BBC4 comedy Detectorists, the aforementioned Capital, and an upcoming ITV drama, Churchill's Secret, in which she plays the daughter of Winston Churchill (portrayed by Michael Gambon). She's also just completed filming with Gemma Arterton and Sam Claflin in an adaptation of Lissa Evans' novel Their Finest Hour and a Half, about a wartime British propaganda film crew.
"I play this acid-tongued script editor ... lesbian, but no sex," she says.
Stirling also has a new "boy" - Elbow's feted singer-songwriter Guy Garvey.
"It's amazing," she says. "I come from huge privilege and he comes from seven kids in a small house in Manchester and a pretty tough upbringing, and somehow, politically, morally and humour-wise, we meet in the middle."
Her "poshness" has, she thinks, lost her as many parts as it has gained.
"I won't change the way I talk for anyone. I'll do it for work, but not because I think someone will like me more if I take the edge off."
Stirling is taking the rest of the year off to recharge, but she is now so confident in her own distinct place in the thespian universe that she is unafraid of sharing screen time with her mother - first on an episode of Doctor Who and now in Detectorists (in which Rigg plays her mother).
"Now she needs to get me a part in Game of Thrones and we'll be quits," she smiles.
Capital begins on BBC1 later this month