"Aw ... ah wanted the radge tae gist f--- off ootae ma visage, tae go oan his ain, n gist leave us wi Jean Claude. Oan the other hand, ah'd be getting sick tae before long, and if that c--- went n scored, he'd haud oot oan us."

If you have problems understanding this passage from Trainspotting, imagine how Americans will fare when the film is released there in July. Fearing that audiences will find the Edinburgh vernacular incomprehensible, Miramax, the film's distributors, have asked its British producers to dub it in parts.

The film's actors were initially resistant to changing their original performances, but were persuaded by producer Andrew Macdonald that it would help sell the film in America.

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He insists that the changes are not fundamental. "It just meant cleaning it up so the pronunciation is clearer," he says. "We've concentrated on the first 20 minutes to give people a chance of getting into it. We didn't want them to reject it from the beginning. After that, they either get it or they don't."

Miramax describes the doctoring as a "slowing down".

American readers also are being helped with Irvine Welsh's original novel, which is to be published with a glossary to coincide with the film version's release. Gerald Howard at New York publisher WW Norton compiled the glossary with some help from the author.

"It's not an easy read for an American," says Mr Howard. "The glossary will help, but in any case the book works a good deal like Anthony Burgess's A Clockwork Orange - if you stick with it for 20 pages you catch the rhythm of the language."

Many of the words explained in the glossary are relatively common British slang - bevvy, dosh, gaff, giro and rat-arsed. But there are plenty that would bemuse most other English-speakers as well: "biscuit-ersed" (self- pitying), "coffin-dodger" (senior citizen), "draftpaks" (nutters, low life, or a container for alcohol) and "square-go" (a fist fight with no knives or barstools). The Paris Review, a literary magazine, is printing the glossary in its June issue, so it may well become a cultural artefact in its own right.

Sally Hibbin, a producer at Parallax Films, accuses Americans of being lazy about foreign accents and dialects. "We've struggled to listen to God knows what accents here, all sorts from all around America, yet they can't take the time and trouble to understand ours," she says.

She has produced Ken Loach's last five films, all of which have sunk without trace in the US. She blames the distributors for insisting that Loach's films be dubbed or subtitled. "The kind of performances Loach gets, which are very emotional, lose all their character when you dub."

Matt Mueller, the American-born editor of Premiere movie magazine, says he's not surprised that Miramax has decided to dub Trainspotting. He watched the film with American friends who "had a really difficult time understanding it".

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"I suppose it's rather patronising to American audiences, but sadly it is true that they have problems understanding different accents."

The British film industry seems to agree that Americans can't understand any English but BBC-style received pronunciation. The Commitments and Shallow Grave, which was also made by Andrew Macdonald and director Danny Boyle, are thought to have flopped in the US because of difficult Irish and Scottish accents.

Although dubbing may be painful for British film-makers, it may have been the key to commercial success for films shown in the US in the past. My Left Foot, In The Name Of The Father, Hear My Song and Local Hero were all partially dubbed.

Riff-Raff was shown with subtitles and Gregory's Girl was completely dubbed, using different actors. Andrew Macdonald says the fake Scottish accents in the latter were unforgettable, "like Sean Connery or Scottie off Star Trek. But," he points out, "the film was a great success there."

Mad Max was also a big success in the US, but only after its original Australian accents were replaced with American ones.

Ms Hibbin suspects that beyond the barrier of accent, the real problems that Americans have with Loach's films are cultural, that they are "very British and deeply political". Americans seem to prefer films where Britain is preserved in aspic, either in an Edwardian heyday or in the twee world of Four Weddings and a Funeral.

Welsh's depiction of Scotland's junkie subculture may come as an unwelcome shock, regardless of how the characters speak. American ignorance about Welsh's world was revealed last week during the Cannes film festival. One headline ran: "Author of Trainspotting drug novel tried heroin."

Next we'll be hearing that William Burroughs once smoked a joint.