As one of the few middle-aged men in the country who did not catch so much as a glimpse of the BBC drama Tipping the Velvet - the "Victorian lesbo-romp", as it was characterised in at least one tabloid newspaper - I am at a disadvantage waiting for Rachael Stirling in a busy bar on London's Haymarket. Neither of us knows what the other looks like. Which is why, when she does arrive, she approaches the wrong man and says a bright "Hello!". He looks pleasantly surprised. He's doubtless one of those who did watch Tipping the Velvet.
Anyway, the misunderstanding is quickly sorted, but it hasn't helped to ease Stirling out of her flap. She is, I think, the flappy sort, though in an ultra-confident, loud, rather engaging way. She rummages in her bag for a packet of Silk Cut, and gets cross with her mobile phone. "Shut up," she says, as it starts to trill. "SHUT UP!"
We talk, as we are obliged to do, about Poirot, in which she appears on Sunday evening, cast very much against type as a quiet, withdrawn woman who is accused of murdering her husband. "I read all of Agatha Christie's books as a child and adored them," she says. "Apparently, after Shakespeare and the Bible, hers are the world's biggest-selling books. Isn't that astonishing?" I point out that perhaps Christie has now been usurped by J K Rowling. "Oh, yes. Oh, isn't that depressing. Fuck, how depressing!"
Stirling swears quite a lot, in that casual, very plummy, public- school way. For a young woman of 26, still finding her way in her profession, she seems formidably self-assured, which I suspect comes partly from a boarding-school education, and partly from being the only child of Dame Diana Rigg - whom she resembles around the dark brown eyes - and the wealthy landowner Archie Stirling.
Does she think that she was a spoilt child? "Oh yes, but spoilt with a great deal of love, really. I have two older brothers, but of Ma and Pa's union, I'm the only product."
Does she ever wish that she did not have such a privileged background? After all, her close friend and co-star in Tipping The Velvet, Keeley Hawes, who sounds similarly posh, actually derives, like Eliza Dolittle, from working-class stock in Marylebone. Which gives her street cred. Stirling has avenue cred, which doesn't always count for as much in the acting world.
"Yes, yes," she says, excitedly. "I know what you mean. I remember auditioning about three years ago and almost seeing the directors' eyes glazing over when I started speaking in this voice. I can't remember who was shit- hot at the time to make the balance swing that way, but I knew as soon as I opened my mouth that I had failed to get the part.
"The annoying thing is that I'm good at accents. I do a bloody good American accent in this [she gestures across the road to the Theatre Royal, where she is currently appearing as Hester in Oscar Wilde's A Woman of No Importance]. That's what made me so cross when I was given so much shit about my accent in Tipping the Velvet. It was an 1880s Whitstable accent that I had really studied; the vowels are slightly longer than in EastEnders. So, when some twit like Lorraine Kelly said, `Why does she talk like Dick Van Dyke?', I thought, `Why don't you go listen to 1880s Whitstable, missus?'."
Lorraine Kelly attempting 1880s Whitstable - now that would be a treat for the nation. As for whether Tipping the Velvet itself represented a treat, opinion was divided. Oddly, Andrew Davies' adaptation of Sarah Waters' novel was received better in America, Stirling says.
"Over there, it was treated as an art- house piece. They celebrated the oddity and bravery of it, rather than letting the dildo [which Stirling wore, strapped on] overshadow everything else. Mind you, it was quite big!" she adds, with a giggle.
She lights up another Silk Cut. "I truly never thought that the dildo would cause such a stir. We'd already had Queer As Folk, and they were licking each others' cracks in that. I never thought that two women having a snog would cause such a fuss."
The fuss continues to yield some decidedly dubious "fan" mail. "There are some really filthy ones that somehow get through to me. I have to tweezer them into the bin. Always from boys, never women." And the fuss hasn't helped, either, in the way that she is perceived in the industry. "I got sent all sorts of scripts that involved flashing your wops on page two, for no apparent reason." Another merry giggle.
Still, the publicity also brought her to the attention of some more enlightened casting directors. And she has been careful to choose roles that differ radically from Nan, her character in Tipping the Velvet, not least Hester in A Woman of No Importance, an earnest, puritanical American heiress.
She is halfway through the run of A Woman of No Importance, and it has been hard work, though she refrains from describing it as "gruelling" because: "I told someone in an interview that it was gruelling, and I've since had the piss taken out of me non-stop. But it is a mental battle. You have to stay chilled and calm during the day, which I'm not very good at, in order to save all your energy for the evening."
She has learnt a great deal, she says, from the production's stars. "Pru [Scales] is a comic genius, and Rupert [Graves] just goes for it head first every night. It's like playing tennis, you have to put a different spin on it every once in a while, because there's a live audience there and you must involve them, gauge what's interesting them and what isn't."
Is her mother a critic of her work? "Oh, yeah, baby, is she. But a wonderful one. I have learnt from her to enjoy being given notes [of criticism], and I had quite strict notes from her for the first few things I did. But they've got less, which is a good thing.
"She came to see this play quite early on, and afterwards I was due to meet her at Sheekey's. I was really nervous, and at the interval I asked the front-of-house manager how she was getting on. I'd asked him to get her pissed, which he did. He said, `It's OK, no notes'. I thought, `Yeah, that's what she's telling you...'. Afterwards, I ran round the corner and arrived all flustered at Sheekey's, and the waiter said: `She's over there. Don't worry, no notes'."
When the roles are reversed, Stirling sits in the theatre watching her mother in awe, she says. "I positively burst with pride at what a wonderful stage actress she is, just gobsmackingly wonderful." The greatest, does she think? "Er, oh, at parts such as those in Mother Courage and Who's Afraid of Virginia Woolf?, yes, yes, I think she is."
It must, therefore, have been unnerving, I venture, going into the same profession. "Yes, but it was the only thing at school that got my juices flowing. And I believe so strongly in my own identity, I'm such a different kettle of fish to Ma. If I saw myself as a tributary of her, then I'd invite comparisons. But plumbers' sons do quite often become plumbers, don't they? You grow up with a certain knowledge of the business.
"I have a strong memory of Mama doing Follies at the Shaftesbury, when I was 11. I went to see her in her dressing-room, which of course is the most exciting place on earth. There are some back alleys of London that belong only to people in the theatre, you know. Only they know where the stage door is, for certain, of these wonderful theatres. The alleys around the back of Wyndhams and the Albery are Dickensian still. Almost untouched. That struck me very much as a child."
She has recently become acquainted, she tells me, with another building redolent of Dickensian times: Crumlin Road prison in Belfast. It was there that Freeze Frame was filmed, a low-budget psychological thriller in which she plays a newspaper reporter trying to uncover the details of a 10-year- old murder, apparently committed by a paranoiac played by, of all people, the comedian Lee Evans.
"It's Lee's first wholly straight part," she says. "And my part is dark, dangerous and bloody scary. The emotional territory it goes into is vile, and I couldn't shake it off, not when we were filming in Crumlin Road, which is a disused but still intact prison. Even the gallows are still intact."
Freeze Frame is due for release in February. "Lee and I thought that it would open in one cinema in Peckham, or whatever, but Universal has bought it, and is giving it a huge distribution."
Whether or not Freeze Frame does well, there seems little doubt that we will be getting to know Rachael Stirling very much better these next few years. Not that she wants us to know much about her private life, revealing only that she is currently single. Her long- term boyfriend, John Lycett Green, reggae DJ and grandson of Sir John Betjeman (what a marriage of dynasties that would have been...) recently ended the relationship, reportedly because he couldn't cope with the Tipping the Velvet brouhaha.
"But I'm a very happy bunny. And will you say that I play in an all-girls football team called Frisky Town? We play under the Westway in Ladbroke Grove, and I love it. I'm in defence, but I have been known to sneak forward."
I can't say I'm surprised.