"Happy-Go-Lucky" is something different from virtuoso British writer-director Mike Leigh. For what feels like the first time in his more than 35 years of bringing insight and intensity to the exploration of human behavior, Leigh has put a thoroughly happy person front and center in one of his films.

That's not to say that Leigh's earlier films, including "Life Is Sweet," "Naked" and the more recent "Vera Drake" and "Secrets & Lies" (both of which earned multiple Oscar nominations), were lacking in humor or happiness. But no one with Poppy's particular kind of effervescent presence has been on offer in Leigh's world or, for that matter, anywhere.

Played by Sally Hawkins in a performance that won the Silver Bear for best actress at the Berlin Film Festival, Poppy practically defines irrepressible. With a personality as distinctive as her wacky clothing style, Poppy is the kind of person who completely means it when she says "Hello there, cheer up" to a flower whose head she stops from drooping.

As opposed to the fake cheerfulness of sales people and service staff, Poppy's good humor comes off as both genuine and disconcerting. She is a person open to life, open to experience, someone with a centeredness and sense of balance that keeps her from getting more than temporarily down.

As is always the case with Leigh's protagonists, Poppy does not fit into a schematic log line; she simply is. She exists with an intensity that few other filmmakers' characters can manage because of the singular way Leigh creates his people.

The director has called his method "organic," as in "growing properly rooted and centered." What that means is spending enormous amounts of time, sometimes months, in one-on-one work with the actors creating characters literally from scratch. Once Leigh decides that his people are at the appropriate stage of readiness, the director brings them together for more months of extensive improvisations before a final script is nailed down and filmed.

So while it is possible to describe Poppy as a curious, game-for-anything London primary school teacher who shares a flat with fellow teacher Zoe (Alexis Zegerman) and likes to unwind on the trampoline, the fact that she is a complex person and not a conceit makes all the difference.

Although "Happy-Go-Lucky" follows a progression in Poppy's life, it also functions as an episodic scenes-from-a-life type film where we are in effect eavesdropping on situations that can go from humor to fury in a heartbeat.

Because Leigh works that way with all his characters, even those who turn out to be minor — like a determined flamenco teacher (Karina Fernandez) and a disoriented street person (Stanley Townsend) — all have an emotional texture that makes us sit up and take notice.

The central interaction of "Happy-Go-Lucky" turns out to be, likely as much to Poppy's surprise as to our own, the one between her and Scott, the instructor she hires from the Axle School of Motoring to teach her to drive after her bicycle disappears.

Exceptionally played by Eddie Marsan, Scott is Poppy's opposite in every imaginable way. Dour, disgruntled and deadly serious, with a teaching style and philosophy that are outside of Poppy's experience, Scott is exasperated almost beyond words by his new pupil. The way these two characters react to each other while staying completely in character displays Leigh's method the way nothing else can.