But the most distinctive element is the mood of the room: expectation. The usual journalistic rustling feels a bit hushed, especially as they announce the arrival of our special guests. In stride Rob Reiner, Morgan Freeman and Jack Nicholson, all looking like the wealthy, successful stars that they are. Reiner seems to be enjoying the fact that he's not the centre of attention. Freeman is uber-relaxed in crisp jeans and a blazer. Nicholson is grinning in a salmon polo shirt, wearing big sunglasses and immediately lighting up a cigarette, even though he clearly knows Britain has a no indoor smoking law. No one says a word.

It's the day after Heath Ledger died, and the topic is raised instantly. After all, Nicholson is the previous incarnation of the Joker, and Freeman costars in The Black Knight, although they had no scenes together. None of the three men had met Ledger, but all had personal connections with his tragic death. Reiner remembers working with River Phoenix on Stand By Me; Freeman clearly has admired Ledger's work over the years; Nicholson offers a cautionary story about his own experiences with sleeping tablets, and how he warns anyone who will listen about the dangers.

The mood is sober, so even though we're here to talk about a comedy, we begin talking about the film's depiction of grief, and specifically the scene in which Nicholson bursts into tears. "All I did was just let it take off on me," he says. "I was just standing there looking at the pictures on the dais, and the tears came. I liked the film's poles - from being slapstick to doing the eulogy."

"To see him as vulnerable as he was is a testament to how talented he is," interjects Reiner. "He's an artist!" When a Finnish journalist in the front row asks a question, Nicholson can't find her in the bright lights and is clearly distracted looking for her. "Were you asking me?" he asks deadpan when he finds her. "What was the question again?"

It's about what they would put on their own bucket lists, and Freeman answers first. "I've just recently taken up golf, so most of the things on my list would have to do with golf," he says. "And I am quite enamoured with my business jet. And if I was going to say who I would like to have met, I'd have to say Diana."

Nicholson chimes in: "It would be exactly the same for me, except that I did meet Princess Diana - a charming woman," he smiles knowingly. "I always wanted to see my children graduate, to speak another language, learn to cook." To illustrate his cooking prowess, he tells a story about working as a short-order cook in New Jersey, when he served two pancakes to a customer, who complained that they were too thick. "I told her to make her own god-damn pancakes!" he laughs.

And Reiner takes the publicity line: "I always wanted to work with these two actors together - the two best in the world. They come prepared to play - nothing threatens them. It's like a dream come true."

The conversation stays rather serious, as they begin talking about where we can touch happiness in life. "Finding joy is tantamount to finding yourself," Freeman says. "It's about being comfortable in your own skin. And that's like, well, ice cream!"

Reiner laughs: "Morgan is like a Zen master. I've never met anyone more comfortable in is own skin! For me, I'd say happiness is with my wife and children. There's no feeling of love more powerful than that. Everyone is born with the knowledge that they're going to die, and what we have to do is find the joy."

Nicholson has zoned out again. "What was the question again?" he says mischievously. "There's some joy to be found every day," he adds. "I took particular joy the other day in the faces of all the pundits who said Hillary Clinton's campaign was dead in the water after the first primary! And I took joy in watching my daughter in a play recently." He goes on to talk about a recent golf game that found him lying in a sand trap throwing a tantrum.

So of course the conversation drifts to aging. "Your priorities change whether it's because of your character or because of a loss of facility," Nicholson says wryly.

And does it get hard to find good roles as you get older? "Literature is kind of limited for characters over 50, and I never want to get trapped in a kind of role," he says. "I also never want to repeat a success, because if you do the same thing three times, you're trapped in that kind of role. So I tend to play characters who are older than me, rather than younger. I always look for a vacuum to fill, to break the conventional wisdom, to bring sexuality into middle age! As opposed to the Father Knows Best kind of movie, where they have all those kids but they somehow never seem to take their pants off."

He continues: "But that's the only area of conscious shaping I've done in my career. In The Departed I wanted to bring sexuality to the role, and I might have overdone it. But I don't think so. "

Meanwhile, Freeman is sinking into a Zen-like trance. So someone asks him if it's true that doing comedy is more difficult than drama. He calmly turns his head and says, deadpan, "I don't do comedy."

Once the roar of laughter settles (Freeman hasn't flinched), the conversation turns to whether there was a temptation to try to steal scenes from each other. "You can't work against another actor," Freeman says. "You have to fall back on them."

"I always assume the other person is perfect in what they're doing," Nicholson adds.

"The greatness of these two," says Reiner, "is that they understand that giving the best brings both games up. Once they're on the stage, they're ready like horses at the starting gate. I shot most of the film in one take - two, three at the most. it was perfect. Of course, a lot goes in before that first take, plenty of sturm und drang, but once they hit the stage, they're ready."

"I remember saying to Stanley Kubrick on The Shining, who did hundreds of takes, 'If you think take 100 is it, just wait until 101!" It was just to psyche him out, but there's always something you can find for the next take. And sometimes you had to do a bad take in the 20s just so you weren't there all day."

He says the fact that The Bucket List is a two-hander made a big difference in the filming process. "There's a certain simplicity," he notes. "It's all on you. You're not running or screaming. It's not pyrotechnical. It's the script, and it's subtle so you have to just bring it. I think simplicity is often overlooked."

One of the film's memorable moments is the timeless advice: "Never pass a bathroom, never waste a hard-on, never trust a fart." Do they have any advice they'd like to impart? "Well I'd say don't lie, don't steal and don't be afraid," Nicholson says.

"Mainly don't be afraid," Freeman adds.

CLARIDGES, LONDON, 23.JAN.07