TOPSY-TURVY-- ***1/2 -- Jim Broadbent, Allan Corduner, Timothy Spall, Lesley Manville, Ron Cook, Wendy Nottingham, Kevin McKidd, Shirley Henderson, Dorothy Atkinson, Martin Savage; featuring the music of Gilbert & Sullivan; rated R (nudity, violence, vulgarity, mild profanity, drug use); Loews Cineplex-Odeon Broadway Centre.

One of the true delights of "Topsy-Turvy" is that, to be enjoyed, it doesn't require either appreciation or knowledge of its subjects, masters of the comic opera William Schwenk Gilbert and Arthur Sullivan.Not that it would hurt. In fact, those who are well-acquainted with the duo and their works -- "HMS Pinafore" and "The Pirates of Penzance" probably the best-known -- are likely to love this sumptuous feast of music and mirth.

But even neophytes should find something to like about this warm and light-hearted biographical comedy-drama from British filmmaker Mike Leigh, who's been on something of a roll lately (with this movie, "Secrets and Lies" and "Career Girls").

Admittedly, at 160 minutes, it's probably too much of a good thing. But, given that so many of the film's scenes consist of productions of Gilbert & Sullivan musical numbers, who's going to complain?

The story is a fictionalized account of how Gilbert and Sullivan came to write "The Mikado," the lively 1885 piece that marked a rebirth of their popularity with both British theatergoers and critics.

However, this particular collaborative effort isn't an easy one. Composer Sullivan (Allan Corduner) is loathe to work with lyricist Gilbert (Jim Broadbent) again, believing his writing partner's work has become too formulaic and contrived -- or as the reviews have noted, too "topsy-turvy."

Instead, he longs to go his own way and, hopefully, write more serious compositions. Unfortunately, both men are contractually bound to the Savoy Theatre, and impresario Richard D'Oyly Carte (Ron Cook) isn't about to let them get away without at least one more play.

And while the interested parties seem to be at an impasse, it's the still-fuming Gilbert who manages to save the day. Dragged reluctantly by his wife (Lesley Manville) to a Japanese exhibition, he is inspired to write "The Mikado." And even more astonishingly, he somehow convinces Sullivan of the worthiness of the concept.

Then the really difficult part begins, as the duo has to oversee its staging and production -- all the while having to deal with temperamental cast members and even bigger annoyances.

It's probably not too surprising that Leigh, known for his meticulous filmmaking efforts, has re-created the period perfectly. What is surprising is how much the tone of the movie is completely in keeping with that of Gilbert & Sullivan's best works.

Leigh has also written a verbally spry script that affords many opportunities for a talented ensemble cast, which includes such Leigh-movie regulars as Broadbent, Timothy Spall, Manville and Alison Steadman.

Although Corduner and Broadbent -- who neatly avoids making Gilbert seem like a buffoon -- have the meatiest roles, Spall and Manville nearly steal the film from under them with fine supporting turns.

If the film does have a problem, it's the sometimes too-leisurely pace, since more than a couple of scenes start to drag. Fortunately, every time that happens, the film is buoyed up by sumptuous renditions of several "Mikado" songs.

"Topsy-Turvy" is rated R for female nudity, scenes of stage violence, some crude humor, scattered mild profanities and a brief scene of simulated drug use (heroin).