This is a woman who jealously protects her privacy. "I don't feel I should be up for grabs," she says, pointedly. "Nobody should be, unless they absolutely set themselves up for it. At best what performers do is a public service, but that still doesn't mean you're up for grabs."
Some journalists have found this guardedness frustrating. She doesn't subject herself to many interviews, and it's clear that she finds the whole ritual about as comfortable as an hour on a bed of nails. Epithets such as "difficult", "cranky" and "dull" have been attached to her. In one journalist's assessment, "our Miranda does not give good interview... She is quite the human clam". I felt particularly nervous about her comment: "Although I have objected to the occasional thing that has been written about me, I've never taken a swing at anyone. Not yet, anyway."
Without resorting to physical violence, Richardson admits to wariness around journalists. "Sometimes you're open with them, and you get horribly traduced," she sighs (she does a lot of sighing). "I'm deeply bored by that."
But steer away from her private life - she lives alone in west London with her cats and an axolotl, since you ask - and on to the subject of her work and she is transformed into the "wonderful, spectacular" creature the fan raved about. Then, much as she does on stage, or screen, she lifts her gaze and her eyes gleam with passion.
Richardson's greatest gift as an actress is to clothe herself so seamlessly in a role that you can no longer see the join. It is not hard to understand why she has been described as "Britain's answer to Meryl Streep".
Think of the scary intensity she brought to such roles as TS Eliot's disintegrating partner in Tom and Viv, or the bitterly wronged wife in Damage - both of which earned her Oscar nominations. One critic gave her the apt title of "the most combustible actress of her generation". According to Mike Newell, who directed her in her memorably deranged debut, Dance With a Stranger: "She is someone who lives on her nerves a lot of the time. It's extremely exposed and very subtle, and comes from very detailed observation. She is like a windchime - she holds herself up to all the emotions that are blowing."
Currently, Richardson is captivating audiences with a portrayal of a seductively right-wing woman in Aunt Dan and Lemon at the Almeida Theatre in London. Next week she will be enthralling us in a different medium with her performance as the mischievous Miss Gilchrist in All For Love, a lav-ish BBC1 adaptation of Robert Louis Stevenson's unfinished novel, St Ives.
When Richard E Grant's inept soldier tries to woo her with the line, "Miss Gilchrist, may I say that your beauty maddens the soul like wine?", she replies quick as a flash: "No, you may not." As he goes on to inform her that his first name is Farquhar, she says "how charming" with as much scorn as it is humanly possible to inject into two words. Nobody does withering contempt better.
So just how does she "become" someone else? "You try to get inside someone's thought process or under their skin," she explains. "It's to do with compassion - you have to feel what they feel."
Initially, she found it difficult to work her way into the psyche of the insidious Aunt Dan - "I said to Wallace Shawn [the playwright], "this is not like slipping on a comfy jacket" - but she soon located the key to the character's wardrobe. "I didn't suddenly lose a lot of friends and become a raving lunatic at Speakers' Corner," she laughs. "I just began thinking about the banality of evil. Monsters are close to home."
Trained at the Bristol Old Vic, Richardson claims there is no Method in her method. "I haven't got a house full of dogs and children, so I've got time to let things float into my head. There's a point where you fall in love with whatever you're working on. It just gets into your mind, and you find yourself muttering lines to yourself."
Nevertheless, she refutes any suggestion that she becomes immersed to the exclusion of all else. "I don't go on living these people. There's too much else going on. I can leave these characters at the theatre or on the film set. If I was so wrapped up in them, I'd have been run over by now."
With her blonde hair scraped back to highlight piercing, blue-grey eyes and exquisite, porcelain features, Richardson is an austere beauty who could easily have made it in Hollywood. But although she has appeared in a number of well-regarded American indy films - Robert Duvall's The Apostle, say, or Kansas City by Robert Altman - the 41-year-old actress has never responded to Hollywood's advances. She famously turned down the part which Glenn Close eventually took in Fatal Attraction, succinctly pronouncing it "crap".
"Those sorts of parts demonise women," she says in a tone that brooks no contradiction. "I don't know what it would have taken for me to become mainstream Hollywood, but I don't think for a moment it would have suited me. Anyway, where are the scripts? They're usually pretty disappointing."
Hollywood's demands for a "star persona", easily recyclable in film after film, would also have vitiated against the element that distinguishes all Richardson's performances: surprise. So often her roles jolt audiences with a short, sharp shock. "I want to surprise myself," she says. "I'd get bored if I was always the same thing. There are people who virtually play themselves every time. They're loved for that, and that's what people expect. I'm not one of those people."
Next she is looking to play someone "if not fluffy, then at least charming - because Aunt Dan is certainly not charming". A comedy would not go amiss. One of Richardson's finest hours was as the deliciously batty Queenie in Richard Curtis and Ben Elton's BBC1 sitcom Blackadder. "It was just bonkers," she recalls fondly. "The scripts had a very tight balance between Richard's gloriously detailed historical almost-truths and Ben's not-quite toilet humour."
Even in her darkest work, Richardson has always tried to let in flashes of humour. "That shows a roundness of experience," she says. "Those moments of lightness and irony punctuate anyone's existence. In comedy are the seeds of tragedy, and vice versa."
Zealous about her work, Richardson can make for intense company. For all that, she possesses a dry-as-dust sense of humour which every once in a while she allows to seep through. She reveals, for instance, that the unsettling nature of Aunt Dan and Lemon has got to the cast. "Everyone has been having disturbed sleep and bad dreams. We've all been clobbered by the weightiness of this play." She pauses before adding with immaculate timing: "Maybe it's just the drugs."
All For Love is on BBC1 on 6 June. Aunt Dan and Lemon continues at the Almeida, London, N1 (0171-359 4404) until 5 June