There are cozy, innocuous pleasures to Nicholas Hytner’s adaption of Alan Bennett’s “The Lady in the Van,” but chief among them is watching two grand old talents – Maggie Smith and Bennett, himself – operating firmly in their self-created wheel houses.

Smith plays the ornery vagrant Mary Shepherd who one day turns up in her dilapidated van on the playwright’s North London block, where she stubbornly remains for 15 years. After taking squalid turns parked in front of different neighbors, she’s allowed by Bennett to settle in the driveway to his townhouse.

She’s a mysterious and cantankerous figure. Sharing her name with few, she explains that she’s “in an incognito position, possibly.” When not impinging on Bennett for a visit to the lavatory, she chases singing school children, paints her rundown van yellow and skulks around, a cranky ball of rags and plastic bags. There are hints of a past as a nun, as well as an old sin that haunts her.

In short, Shepherd’s irascible peculiarities are tailor made for Smith, who’s given all manner of things at which to disgustfully wiggle her nose – the trademark power of Smith’s that’s no less potent as a foul homeless woman than as the dignified dowager of “Downton Abbey.” She can condescend, magnificently, from any height.

Smith played the role before in the 1999 play “The Lady in the Van,” which was also directed by Hytner, a regular hand of Bennett movie adaptations (”The History Boys,” ‘’The Madness of King George”).

But the play wasn’t the start of “The Lady in the Van.” It comes from Bennett’s own life. The story is mostly true: Shepherd really did turn up on Bennett’s Camden block, like a prepackaged story for the playwright. He wrote about her first as diary entries for the London Review of Books, then as a short memoir.

Bennett turning the experience into art is a central part of “The Lady in the Van,” too. He has split himself into two (both played by Alex Jennings): “The writer is double,” he narrates. “There is the self who does the writing. And there is the self who does the living.” The film was even shot on location, on Bennett’s actual driveway.

It’s all a very twee setup and not exactly the sort of thing that sets the world ablaze. But at least until the fanciful finale, there are few false notes in the sturdy, pleasantly entertaining “The Lady in the Van.” It unfolds as an investigation into Shepherd’s unexpected past and a reflection on Bennett’s own motivations as a writer.

“The Lady in the Van,” sweet and sure-handed, is less timid than it appears, though, and Hytner’s film is ironically aware of its own modest position. “So English,” one visitor says of Bennett’s latest play. “Just what people want.”

“The Lady in the Van,” a Sony Pictures Classics release, is rated PG-13 by the Motion Picture Association of America for “a brief unsettling image.” Running time: 104 minutes. Three stars out of four.