Two factors work against "When Did You Last See Your Father?" from its outset.

The movie falls victim to the epidemic vogue for jumbling past and present, intermixing the two to keep viewers guessing - an overworked plot stratagem that plagued the otherwise excellent "La Vie en Rose," for instance.

Also, an intimate look at a son grappling with his aging father and coming to terms with their life of conflict is achingly familiar, recalling "I Never Sang for My Father," "Long Day's Journey Into Night" and "Death of a Salesman" - mythic matter as pop-worn as Harry Chapin's "Cat's in the Cradle" and dating back to Oedipus. For a time in this latest entry, the barbs back and forth - the impotent frustration of a son at odds with his father's materialism and philandering - herald the trite.

But ever so slowly, and certainly by his heart-tugging finish, director Anand Tucker wins you over, delivering not another imitation but a very persuasive drama. He's armed with two potent weapons, beginning with a strong cast. Jim Broadbent and Colin Firth demonstrate once again the magic and majesty of finely etched British acting. Backed by a solid support cast, their performances are deeply felt and cagily detailed.

Secondly, as he proved in "Hilary and Jackie," Tucker has an inimitable flair for dissecting family relationships. He walks up to the edge of sentimentality and then steps back. He wields a surgeon's scalpel, not just at the core but at more remote tissues of the parent-child dynamic, exposing anger, self-deprecating humor, resentment, misunderstanding and love to the light of day. The disturbing, embarrassing domestic moments and conflicts are quirky, slightly weird, and yet they boast the shock of recognition because they're so true to the strife in every family.

Adapted from the 1993 book by Blake Morrison, inspired by his own father, the story tells of Arthur (Broadbent), an amateur con artist who loves to trick his way into racing events or cut to the head of a traffic line by sailing along the road shoulder. His family life bears some of that same deception. He's carrying on a longtime affair with a woman whose daughter may be his own, and his approach to his son Blake (Firth) is one of callous, manly disdain. "Fathead," he calls him, teasing him tactlessly about sex and just about everything. His idea of camping involves forgetting key equipment, blaming his son and laughing when rain waters flood their tent.

Blake, by contrast, is a sensitive boy who grows up to be a writer, cowed by his father's bluster and wounded by his adultery. They are archetypal mismatches - Blake the sensitive, introverted poet, Arthur the financially solid braggart and charmer. They find meeting points only sporadically, at odds even during Arthur's cancer and death, events Tucker observes with steely realism.

Firth is subtle, understated, a master at holding back roiling sentiments with earnest, painful looks. But the real star is Broadbent, portraying Arthur as a kind of jaded St. Nicholas with the irrational glee of Mr. Micawber and the dark mischief of Fagin. The movie's strength is that even death doesn't render final resolve. The catharsis here is all the more moving because of what wasn't finished, what remained unsaid and what in the answer to the title's question proves unknowable.