When Shrek 2 opens here in July, British viewers will see a different version from the one showing in American cinemas. No, there won't be an extended, extra-violent climax, à la the "House of Blue Leaves" sequence in the Japanese cut of Kill Bill Vol. 1. Nor will there be bonus explicit footage of Shrek and Fiona playing Pin the Tail On the Donkey for a "European" cut, in the style of The Man Who Fell to Earth. This is a children's film, for heaven's sake.

When Shrek 2 opens here in July, British viewers will see a different version from the one showing in American cinemas. No, there won't be an extended, extra-violent climax, à la the "House of Blue Leaves" sequence in the Japanese cut of Kill Bill Vol. 1. Nor will there be bonus explicit footage of Shrek and Fiona playing Pin the Tail On the Donkey for a "European" cut, in the style of The Man Who Fell to Earth. This is a children's film, for heaven's sake.

No, Shrek 2's changes for the UK market are small but significant. Two of the characters have been revoiced for British prints, so that American celebrities doing walk-on (or should we say, "talk-on"?) parts have been replaced by British ones.

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The first switch involves Ugly Sister 2 ( above), an obvious man in drag who runs the dive where Fiona's treacherous father goes to hire Puss in Boots (Antonio Banderas) to kill Shrek (Mike Myers). In the US version, Ugly Sister 2 is voiced by the CNN talk show host Larry King, whose gruff, grizzled tones are instantly recognisable to Americans, who see him grilling celebrities and politicians nightly on Larry King Live. UK viewers, however, will hear instead the distinctive, but decidedly less gruff, Jonathan Ross. Given that Ross, far from being a serious journalist, is famous for lisping and occasionally wearing skirts, the gag gains a very different kick. Perhaps Jeremy Paxman said no.

This swap is at least more understandable than the later one, when the British showbiz reporter Kate Thornton replaces Joan Rivers in the role of The Red Carpet Reporter. As most Brits (however benighted) know, Rivers is the grande dame of trash talking, a 70-year-old former Borscht Belt comedienne whose stand-up material predates the French Revolution and whose face has been lifted more times than a Concorde flap. Every year, on Oscar night, she trawls the carpet outside the Academy Awards ceremony, caustically reviewing the frocks of the famous and dishing out insults. That's why her appearance in Shrek 2 - the character is even modelled to look like her - is one of the funniest moments in the American version. Plus, there's no mistaking her throaty, Brooklyn cackle. Thornton, on the other hand, with her giggly, girlish pipes, only works as a joke in the film (and a weak one at that) if you know that it's her doing the voice. And, sorry Kate, most people won't.

Perhaps it's carping to single out the weaknesses of the voice substitutions, given that Shrek 2 is, by and large, hilarious, although perhaps a shade less charming and fresh than the first instalment. Whether the Ross and Thornton substitutions enhance or detract from the film as whole is ultimately less interesting than the fact that they are there in the first place. In a world of ever-increasing homogenisation and globalised cultural product, the attempt to redo bits of a movie to make it funnier for a specific market shows, if not a laudable sort of sensitivity then, at the very least, sound business sense.

The quick-fire, wilfully anachronistic, pop-culture-savvy humour of the Shrek franchise draws mainly on American references to begin with - one could argue that these additions go some way to redressing the balance. Given that all cartoons are eventually dubbed for foreign territories, using different voice actors in cameo roles for the UK version is just taking it a shade further. A source close to the film explains the decision, "was just seen as a fun opportunity for markets that don't normally get the chance to use local talent to participate, albeit for a couple of lines of dialogue only." The English-language versions for Australia, New Zealand and South Africa will do the same.

It's as if we've come full circle, back to the earliest days of sound cinema when different versions of the same film were made for different countries using the same script, sets and costumes, but in some cases entirely different actors. Stars are integral to marketing a film, but with a cartoon like Shrek, the distributors are forced to think locally.

It now looks quite canny of the producers to have cast Banderas as Puss in Boots, not just because his spot-on timing is one of the film's highlights, but also because he can do the Spanish-language dubbing himself. And if another actor is doing the voice of Donkey for all of Latin America, audiences there don't much care if Eddie Murphy was in the US version or not. Incidentally, the guy who does voice Donkey, the Mexican comedian Eugenio Derbez, dubs nearly all of Murphy's films for this market (in Shrek 2, so I'm told, he sounds like "Donkey on speed"). He even came to Cannes for the film's premiere, along with the Japanese actress who voices Fiona and the Norwegian actor who does Shrek, among others.

Perhaps the most pressing questions of all are this: will the Japanese laugh at Princess Fiona having a Justin Timberlake poster in her bedroom if Cameron Diaz isn't doing her voice? And does that Norwegian actor who plays Shrek do the Nordic equivalent of Mike Myers's atrocious Scottish accent? Now there's a case where redubbing might actually improve a film...