Playing a real, living person, inevitably lends an extra layer of complexity to an actor's job. Playing a good friend, one might imagine then, even more so.
Yet the much-garlanded, veteran actor Alex Jennings is remarkably unfazed by the challenge of becoming his mate Alan Bennett on stage and screen.
Bennett features more than once as a character in his own work, so inevitably somebody had to do it. And Jennings has made such an art of representing the writer that he is now practically his official performance proxy.
He has played Bennett on both stage and screen. It is a creative collaboration that started with a series of short plays at The National theatre in London and has now found its way into cinemas.
Jennings is currently starring in The Lady in The Van, the film adaptation of Bennett's autobiographical play, which tells the story of his oddball friendship with a malodorous bag-lady (played by Maggie Smith) who parks the van, in which she lives, in his driveway in Camden and ends up staying 15 years.
"It is weird," Jennings admits. In person, he is tall and tiggerish, with an open, affable face and just a touch of luvvie about him - a far cry from his appearance as the frowning, semi-reclusive playwright in grubby clothes in The Lady in the Van.
"I mean, I have his blessing. So that kind of gives me confidence. Alan has now said he suspected that I sort of always did an Alan Bennett, and I've just now been given the opportunity to go public with it."
Alan, it seems, is not wrong.
"It is sort of true," he says with a laugh. "And I think a lot of people do. Just not professionally".
Bennett and Jennings first worked together in TV quite a few years ago.
"I've known him a long time," he says, and so he had plenty of time to observe him at close range. It helps too that he "grew up watching his stuff on TV. All the stuff that he featured in and also all of his amazing body of work."
So Bennett was present in Jennings' life long before he actually knew him "and my kids grew up listening to his recordings of Winnie the Pooh and Wind in the Willows, which are genius".
During the making of the film, the man himself was around all the time to give feedback and notes.
"He was concerned about me not being too plaintive and wanting me to be tougher. And not doing sort of, cosy cuddly Alan Bennett, because he doesn't like to be thought of as that. He's much sharper than that. Probably because of The Wind And the Willows, people do sort of think he's a bit Moley. And he's not."
He admits that he tends to study Alan when they are together, which must be a bit odd, socially. "I do watch him," he admits. While Bennett confessed to him that sometimes (on set) "he'd see me sort of walking past the window and he said it was kind of spooky for him. I'm not a lookalike, but there is clearly something going on and when I get the hair and glasses on and the tie and the jacket and the jumper. He always wanted them to be dirtier. He put egg down my jumper once. I wear bits of his actual clothes."
Born in Essex, Jennings studied at Bristol Old Vic. Though not quite a household name in film and television, he has won three Olivier Awards and has long been considered a titan of the British theatre scene - almost ever since he was discovered by director Nicholas Hytner (previously the artistic director of the National and now the director of The Lady in The Van) in 1985.
Hytner was something of a mentor, playing a big hand in developing his career and giving him "fantastic opportunities," he says, such as "Country Wife at the Royal Exchange, with Gary Oldman and Cheryl Campbell, and then the Royal Shakespeare Company. I then started to pick up other directors as well, so I don't exclusively work with Nick," he jokes. "But we have a kind of shorthand, I suppose. And he pushes me as well."
Now in his late 50s, he has given the impression in interviews over the years that despite his dream theatre career, he perhaps hankered to do more film and television. Now, with his first starring role in a film and a part in the upcoming big-budget, heavyweight Netflix series The Crown, (currently in production and involving a British film dream team of writer Peter Morgan and director Stephen Daldry), does he feel like that's shifting?
"Well, you never know," he says cheerily. "You can't sort of control it, really. I'm pretty happy with the way it's gone. It's been fantastically varied, what I've done, I suppose. And it's been great to bat back and forth between plays and the telly that I've done and the odd film. I've never played a leading role in a movie, so that's a new thing."
It's an experience that he's enjoying.
"It feels good," he says, grinning. "You get to stay at the Four Seasons hotel in LA and you're very, very well looked after. But I'm grown-up enough not to think of that as the norm."
He did a stint in LA a few years ago to see how it might suit him "very briefly after I did Hamlet for the RSC. I thought I'd go out there after that and see how the land laid," he says.
But it didn't last, mainly because his long-term partner Lesley, wasn't all that keen.
"I'm such a sort of film nerd. I just loved the fact that I was in LA and my friends who I was staying with - I was really lucky I was staying in a really nice place and they were going, 'Mae West used to live there, Bette Davis used to live there.' And I was just like a boy in a sweet shop. And Lesley is much more grounded and practical about all of that."
Perhaps it's not surprising that Lesley is more grounded - she's a landscape gardener by profession. Though she has "always been very involved and is a very keen viewer of what I do and critic of what I do," he says.
The pair have a grown-up daughter and son - an artist and physicist respectively. They make an eclectic and happy-sounding bunch, and this is much, Jennings admits, to Lesley's credit. She was the one to keep the home fires burning, something which "enabled me to go and work in Stratford for lengthy periods of time . . . she has made sacrifices and was there for the kids when I wasn't so much."
The Lady in the Van is in cinemas now.