The Dorset crab arrives in a silver receptacle you can see yourself in, and is much more to her taste than the hubcap-sized starter. There is no buyer's remorse from my side either as the wild boar sausage is as good as you would expect from a restaurant that defines itself with these Ruritanian dishes. You imagine stern Junkers with names like Otto gorging on this stuff before horseback duels in the forest. Though just five years old, the Delaunay is a holdout against the small plate and the sharing concept. It is the bridge between the ossified London that O'Brien came to in the 1950s and the creative destruction of today.
Does she get enough credit for the body of work she has accumulated in between those eras? "A male artist in the room is - for women and men - cultural Viagra," she says. "As for a woman, there may be one or two who are glad you are there but you don't make the same impact." None of this is said with bitterness. If anything, she values being left alone to concentrate on her writing. "For all my affability, I am also cold."
You have to look after number one?
"Well no, you have to look after what is right. In the case of work, you have to look after the work. If someone comes into your life that you don't want and keeps nagging you with emails and things, the gate comes down." She mimes a portcullis shutting in front of her face. This is Graham Greene's "splinter of ice": the chill at the heart of the serious novelist. Writers cannot be with you all that much. And even when they are with you, they are not really with you.
In the 1990s, O'Brien's work widened to take in politics - though, she says in a post-lunch email, it was never about "preaching or protest". House of Splendid Isolation revolved around a member of the Irish Republican Army. Down by the River explored the abortion laws through a courtroom showdown. And in The Little Red Chairs, a charismatic healer who shows up in an Irish village turns out to be a Radovan Karadžić-style fugitive from a dirty war at the other end of the continent. It is her best book (take Roth's word, not mine), a highly evolved writer describing the species at its most basic: a man of violence, a woman driven to folly by want of a child. But there is always humour competing with pain for space on the page. Reading the book, it takes a while to realise it will not be a rural comedy.
"There's a great line in Beckett," she says, searching for a quote to capture this equipoise of light and dark. "I can't remember who says it. 'You're on Earth. There's no cure for that.' There's as much common sense in that as in all of Sophocles or Socrates or anyone else."
She speaks in coherent paragraphs with the rich, sonorous husk of a continuity announcer on a high-end public-service radio station. She is also the most inquisitive person I have interviewed. She wants to know what will happen with this Brexit business (search me), whether I have tried LSD (she has, with the psychiatrist RD Laing) and what pick-up techniques go on in bars these days. Through one of her two sons, an architect who worked on the private members' club Shoreditch House and the Everyman cinema in Hampstead, she still knows her London. She knows her football, too, tuning into big European games of an evening. "When Madrid are playing Barcelona, oh boy, that's a game and a half." She has friends in the adjacent arts, including the film director Michael Haneke and his frequent star Isabelle Huppert (who, it occurs to me, has the poise and the features to play O'Brien in an eventual biopic).
This proliferation of interests makes me wonder why, after all the novels, plays and short stories, she has never been one for essays. O'Brien on Lionel Messi (she rates him over Cristiano Ronaldo), on Emmanuel Macron ("Jupiter himself"), on modern Ireland, would demand attention. I feel like crossing the restaurant to lobby her publisher, who by coincidence has booked a table of his own. "The thing with essays," she says, "is the marriage of theme and writer. If that is vitiated in any way, then the essay is nothing." She contrasts Saul Bellow's powerful early essays with his "cranky" late stuff, when the writer exceeded the theme. If I did not know better, I would detect self-doubt here.
Or it may be that everything she wanted to say in non-fiction form came out with her 2012 memoir, Country Girl. In the book, pride in her defiance of those who sought to contain her - parents, church, spouse - vies with regret at her slowness to act. I press her on which she feels stronger.
"I wish in my early life I had stood up a bit more," she admits, "but all things considered I was pretty brave. You know, if you start off with a pretty terrifying start, you have many handicaps. You have many handicaps." The repetition is poignant. "I would say, as regards my inner self, I am happier than I ever was, while naturally aware of death and decay and decrepitude. I am full of darkness, but I am also full of light. Do you know what I mean?"
Yes. All her readers do.
Memory and language - those precious writerly resources - are flowing as I ask for a coffee. "Because of my religious saturation," she recalls of her younger self, "I believed that mortal man and Jesus Christ overlap. I wanted sensual love and spiritual sensibility. Well, you know what, you can't always have both." Splinter of ice or what.
"You're young, you see," she says, as I settle the bill. "You're happy and you have original life."
Original Life could have served as her memoir title. Her novels are bold, but not as bold as her own story. In literature, characters who escape an unpromising start to make their own way in the world tend to be male: David Copperfield, Julien Sorel, Augie March. O'Brien did not just invert this tradition with The Country Girls and subsequent books, she lived the inversion. The result appears to be a woman in love with the freedom she has won and conscious of what it has cost - but then life, as she says of literature in her email, "requires layers of complexity".
She leaves me with a copy of The Love Object, a collection of her short stories with an introduction by John Banville, her stiffest competition as Ireland's greatest living writer. And now she must head to Chichester. A car waits for her on Aldwych, London's hinge, where postcodes stop starting with W and start starting with E, where tourists, students, diplomats, barristers and chefs on a cigarette break compete for space on the paved bend. Into the scorched traffic she disappears, a city girl.