She allows me to pour her a glass of fizzy water, hoicks herself restlessly about on a chaise longue in a room that was once William Hazlitt's back parlour, and starts to bemoan the unshaven state of her legs.
By rights, she shouldn't really be doing press for LA Without a Map. Her part as Julie - a French actress who goes to LA and winds up waitressing - is little more than an expanded cameo. But her performance - all barks and whoops of dirty laughter - steals the film from under the snub nose of its nominal leading lady, Vinessa Shaw.
She's abetted in this theft by Vincent Gallo, the painter/ fashion model/actor/director with a flair for mad-eyed Reaganite ranting. Gallo turns out to be a rich subject for discussion. I mention that I saw his named carved into a sidewalk near Union Square in Manhattan. "He writes his name everywhere," she says. "He put a sculpture somewhere in the middle of the desert, and wouldn't tell me what it was. Probably a mould of his penis with his name on."
I also mention, more tentatively, that I'd heard he persuaded a former girlfriend to have his signature tattooed on her body. "That's true," confirms Delpy. "She's my best friend. I'd heard all about him from her, which probably wasn't the best introduction." Were her worst fears confirmed? "If you're dealing with someone stupid, and you've heard he's a real badass asshole, then you can be sure it's true. But not someone smart like Vince. The only problem I had with him was that he bit my lip when he kissed me."
Reading through old interviews with Delpy, I was struck by their emphasis on her morbid, pathological side. "I feel so happy when I'm in hospital," she once told Vogue, also confessing that that her first word was "morte" and that she lived in fear of developing a brain tumour. Was this a genuine paranoia, or just an example of a journalist resorting to the Betty Blue-ish cliche of the sexy, neurotic Frenchwoman?
"I used to be obsessed with hospitals," she says. "I used to be an extreme, raging hypochondriac. I used to have panic attacks because I got migraines and didn't know I had migraines. I went blind, saw zigzags, couldn't feel my hands and thought I was dying. Then two hours after having those horrible neurological symptoms, I would get a headache and throw up.
"I thought it was an emotional problem, but one day I went to a chocolate afternoon at Elizabeth Taylor's house ..." Excuse me? "Yeah, a big house party where there was only chocolate to eat all day. There were these solid chocolates in the shape of gigantic, huge firecrackers that were about this big and this thick. I ate three of those bars, literally making myself sick. And I had the worst migraine of my life, and realised what was causing it. I haven't eaten chocolate since."
Delpy has been in movies since she was 14. She made her debut in Jean- Luc Godard's Detective (1985) and spent the next decade trotting between some of the world's greatest directors. She was Bertrand Tavernier's lead in La Passion de Beatrice (1997); took direction from Agnieszka Holland in Europa Europa (1990), Volker Schlondorff in Homo Faber (1991) and Krzysztof Kieslowski in Three Colours: White (1994). Her English-language debut, Richard Linklater's love story Before Sunrise (1997), made boy backpackers pray quietly for her appearance on trans-continental express trains. Then she went back to school - New York University - to learn how to wield a camera for herself.
"The students were a bit resentful, because I was an actress," she explains. But it wasn't her cv they despised - Tom Hanks and Daryl Hannah were in the next class. "All my life I'd been the kid who sat at the back of the class who never wanted to talk, but at film school all I wanted to do was talk. I was the good student who everyone hated - to the point that they accused me of having an affair with the teacher. And at the time I was living like a monk."
Armed with her diploma and 15 years of hands-on experience, she has just directed her first feature: Looking for Genius, a comic mockumentary set in LA. It's now in the final stages of post-production, and she hopes to show it at next year's Berlin Film Festival. "I've tried to follow Kieslowski's example and take my material from real life, not just make references to other movies."
Kieslowski's death in 1996 is a source of guilt. "I felt terrible because I was supposed to join him at a scriptwriting seminar in Switzerland, and I ended up working and couldn't go. You know how it is. Then he had his heart attack, and an Italian journalist rang me up at six in the morning and said, 'So, whaddyathink about Kieslowski's death?'. I was very shocked, and just started sobbing. It broke my heart.
"I know why he died. He was a man who thought nothing could get to him. So he went to the hospital that would do the fastest operation - because he wanted to go ski-ing later. He smoked five packs of cigarettes a day, he had high blood pressure, and he'd salt his steak 20 times. I wanted to protect him, but he didn't let many people tell him what to do. I just hope that wherever he is - heaven or hell - there's a smoking section."
She's less obviously complimentary about Richard Linklater. Delpy claims to have written 80 per cent of her dialogue in Before Sunrise, extracting the heroine's notions about life and death from her own journals. The best scene in the film, in which Jesse and Celine pretend to phone friends at home in order to clarify their feelings for each other, was all Delpy's own work, and based on an experience with a former boyfriend.
"Most people who see this movie think I'm just a dumb actress saying lines, and it's f---ing painful because I wrote every bit of that character, apart from maybe two or three scenes. Sometimes I meet people who've read the original script and seen the movie, and they know how much work I put into it. I'm not resentful but I just want to say it. No one will sue me for telling the truth."
But the experience convinced her of the quality of her writing - at a point when her confidence in this area was in need of repair. "I wrote my first script when I was 18 and then I dated a man who was a scriptwriter, and he broke me to pieces. He was so unhappy that I was an 18-year-old and he was in his thirties, and I'd written this script. He said, 'It was cuter when you just told me the story, because of your little face'."
Needless to say, the relationship did not last much longer. "I'm much more sure of myself now. I've written five scripts in the last three years, and directed my first feature. I'm really a very insecure person, but now I've reached the point where I know that whatever I think of, I can make it. I'm ready. I'm ripe. Like a fruit."
As I'm ushered out of the room by her PR, she's still trying to get a last word in. "I'm ready to fall like a big plum." she calls out. "A big plum!" Then William Hazlitt's parlour door slams shut.
'LA Without a Map' opens on 17 SeptemberReuse content