So feisty American starlet Mary McCormack is holding her shirt up and displaying her . . . er . . . embonpoint to Minnie Driver (and me). "You want a good old-fashioned Wonderbra," she explains. "People make fun of them, but they really . . ." And she demonstrates, cupping her breasts and forcing them skywards. So then Driver - the homely one out of Circle of Friends, remember - juts out her bosom and emulates her colleague; more cupping, more thrusting. Can't they see me? Surely they can't miss the red-faced, sweaty journalist wheezing in the corner of the room.
The two actresses are preparing themselves for the evening's premiΦre of Mel Smith's passable new comedy, High Heels and Low Lifes, in which they star. Somebody has forgotten to bring a brassiΦre with the requisite amount of leverage, and an underling is being briefed in advance of a lingerie forage. Weirdly, the only point at which the two women acknowledge the panting spy in their midst is when Driver has to tell the factotum her bra size. She cackles in my direction and leans forward to write the information silently on a bit of paper.
Driver's munificence in acting out my adolescent fantasies is all the more surprising given recent proceedings. Some few days before this interview took place, her personal publicist, a Ms Van Iden, had demanded that The Irish Times send numerous press clippings to LA for her approval. What can she have been frightened of? Did she fear that I would fill the paper with satirical musings on her client's lurching stop/start career? That I would harp on about the fact that Driver seems prepared to don Prada and turn up for the opening of an envelope?
Anyway, after much stomping of feet and shouts of "we don't do that sort of thing", the issue is settled and I find myself on the way into the relevant room of London's Dorchester Hotel. Suddenly an agreement is thrust into my hands listing a series of ambiguous dicta about what we can and can't do with Ms Driver's quotes Phone calls are made, matters are clarified, and, finally, I find myself face to face with the great star herself. My pencil is sharpened. By God, is she going to get it.
So it comes as an enormous disappointment to discover that Driver is actually quite charming; both intelligent and good-humoured. In a transparent ploy to keep us on the subject of the film - the title of which temporarily escapes me - both actresses are in the room throughout, trading girlish quips and guffawing like Viz's Fat Slags. (Ms Van Iden, please note: this is not to suggest that they are in any way overweight or sexually promiscuous.)
They seem eerily similar to their characters in High Heels and Low Lifes - two ordinary London girls who get sucked into an unlikely scheme to extort money from a gang of cartoon villains. "So I just love this dress. It's got these little straps and every time I see it I want to buy it, and you don't need a bra," continues McCormack. Eventually, I have to cough politely to announce my presence.
"Oh God," exclaims Driver. "How rude of us. How are you?"
And she extends a hand. She is taller than she seems on screen, with enormous eyes, and she must currently weigh about an eighth of what she did when she announced herself on screen in Pat O'Connor's film of Maeve Binchy's Circle of Friends (1995). It is a project she remembers with some affection.
"I loved being in Ireland," she explains. "My family had always gone there for our holidays, so I knew it pretty well. But it was lovely. I came across about four donkeys called Minnie when I was there - very funny."
Despite the film's success, her winning performance as Benny did not immediately catapult her to fame. Hollywood was somewhat blinkered in its approach to an actress who had piled on the pounds to play the film's dowdiest role.
"Well, at the time, I had no knowledge of what doing a role like that might mean," she says. "You only learn these things after a while. At that point, I'd done some telly, a little theatre - not that much really. You're just happy to get the work when a great part like that comes along. At that stage, I didn't think twice about playing this fat girl. But now, knowing what I do, I probably would think twice."
Now, this is interesting. It suggests a calculation about her career that many actors would deny exercising. Some have seen echoes of this in the manner in which this hyper-posh Englishwoman - educated at the exclusive Bedales School, no less - has reinvented herself as an American leading lady. Good Will Hunting (1997), Grosse Pointe Blank (1997), Hard Rain (1998) - in all these films she has abandoned her accent and gone native in a way that few other English actresses have attempted.
"Well, that was where the work was," she says. "For a year or so I really couldn't get arrested. And I went to America on a whim, my agent paid for my ticket and there I was. I don't feel in any way constrained, it doesn't change one's approach to acting. It's just an added aspect to one's career, being plausibly American. I've always been fairly itinerant as an actor anyway. I hope I am plausible."
McCormack says how wonderful Driver is as an American. The two of them then start cackling, and I am left alone with my thoughts again.
Despite appearing in some fine films, Driver has never really been in any kind of sizable hit. If one is brutally honest (oh let's!), she is really best known for her low-cut appearances at awards shows and premiΦres.
I cough again to quieten their chatter. Does she enjoy fame?
"Oh, girls are girls; they love dressing up," Driver says. "There's tons of perks. You can get a table at a restaurant, all that stuff. Of course."
But does she ever want back that piece of herself that is forever public?
"Well, no. If I were to regret it, I would be regretting something that I had relinquished myself. Nobody made me do it. I mean, I'm not so famous that I can't walk down the street or whatever. Is there anything I can't do because of my fame? I'll tell you: I decided that I couldn't take my top off on the beach. There, that's how fame has affected me. But there's nothing you can do about it, it's part of the deal."
Isn't that lovely? You'd never think that Ms Van Iden was lurking in the shadows with her sheaf of cryptic documents.
It's undeniable that Driver has had her fair share of PR crises. Matt Damon chose an appearance on the Oprah Winfrey Show to announce that he was dumping her - the first she'd heard of it. And last year the ubiquitous Van Iden had to deny a premature report about Driver's engagement to boyfriend Josh Brolin ( the news is now official).
"I can't control how people think about me," Driver explains. "I mean, you look at some of the shit they write in the newspapers - no offence." None taken.
"People being titillated is one thing, but out-and-out lies are another. I won't have this. If somebody was running round telling lies about you, would you like that? If you don't control it, it can become like a splatter effect."
Which sounds fairly uncompromising. But, in truth, she seems to be having a whale of a time. With her feet curled up beneath her and her hands flailing about, we could be chatting in her front room.
"Well, this is fun. Because we really like this film and each other," she says. "So much humour about women is either making fun of posh 'It Girls' or big-breasted TV presenters. This is good, honest British humour: intelligent, funny, camp, sometimes ironic. If that makes sense."
And for once, the principals are all female - a rare thing?
"Yes, well that's just the way things are. Usually you have to take a female role that may be quite ordinary on the page and make something of it, make sure they can't cut you out. You have to do everything short of pogoing into other people's close-ups. So it was good that this had real female parts."
And on she chatters, breaking off now and then for a smutty gag with McCormack. It really is hard to grasp what her entourage are so hoity-toity about. Nobody would feel any need to be snide about her if she was just left to be what she is: funny, raucous, normal and - what does that say? - 34B? 34C? God, I wish I could read upside-down.
High Heels and Low Lifes is on general release