Clive James once said that some cultural artefacts are so bland they "taste of cellophane". High School Musical 3: Senior Year makes cellophane taste like chicken jalfrezi. Yet behind the blandness - perhaps even generating the blandness as a symptom - there is something weird and conflicted going on.

This is the commercial apotheosis of the High School Musical brand. The unthreatening Disney teen drama started life just two years ago as a small-screen product, became the centrepiece for a trillion tweenie-girly sleepovers, and now, at threequel stage, merits a fully-fledged theatrical release which might even threaten Mamma Mia's rule at the box office.

Oh. My. God. Going to see it on a date would feel like being the hapless couple arriving in Stepford for the first time: the sheer squeaky-cleanness of everything is creepy, and when the characters are called upon to dance, they do so with robotic efficiency, and sing in that decaffeinated high vibrato, like 21st-century Hollywood castrati. As ever, Zac Efron plays teen cutester Troy Bolton, who totally rules the school basketball court without his artfully contrived fringe ever becoming disordered. Vanessa Hudgens is Gabriella, the talented young singer and dancer with whom Troy appears to be going steady in a sweet'n'innocent way, though the film has a quasi-Bollywood reluctance to show kissing on the lips.

Once again, they find themselves appearing together in the high school musical and Troy even finds that his future in college sports is open to question: should he instead try out for New York's prestigious Juilliard school for the performing arts? The all-important show is once again underpinned by the school's brother-and-sister combo: Sharpay, a Valley-Girl princess played by Ashley Tisdale, and her choreographer brother Ryan, played by Lucas Grabeel, who here looks like the crazed love-child of Will Arnett and Jonny Lee Miller.