Big night out: "The Topp Twins: Untouchable Girls"

Untouchable Girls is an introduction to an act who need some explanation, but finally really are who they are, with few reference points by which to shorthand them - though if we did take up our microscopes and go looking, we might discover some Bizarro World hybrid of the Proclaimers, French and Saunders, and Gilbert and George in their DNA. The Topp Twins, one of New Zealand's biggest entertainment turns, are yodelling lesbian sisters Jools and Lynda Topp. Raised on a farm, the Topps first made their name busking and protesting in the early 1980s before making a triumphant transfer to television a decade later; they presently sell out theatres and festivals worldwide. As one of their writers puts it, the Topps sound like "commercial death" on paper - or, at best, like something that might have washed up on Vic Reeves's Novelty Island. Yet the concert footage director Leanne Pooley cuts into this enjoyable potted history reveals just how adored the Twins are, and how skilled they've become at blurring the entertainment boundaries.

Topp live shows are 50% country-and-Western hoedown, 50% Little Britain-like character comedy, and while the twins were an unapologetic part of the 1980s alternative scene (campaigning not just for gender and sexual equality, but also Maori rights and nuclear disarmament), they remain an act you could take your parents to see without fear of embarrassment, which perhaps accounts for their success. (The Topps' own folks - of traditional yeoman stock, and memorably unsentimental in describing their offspring's coming-out - are themselves ever-presents in the audience by the look of things, serving as vital barometers, for the goal of these shows is not to shock or alienate, but entertain; the twins are one of those rare contemporary acts who would appear to specialise in fostering collectivity and togetherness.)

Between useful archive material (the Topps performed a firmly out number at the New Zealand Music Awards back in 1982, which you suspect the '82 BRITs or Grammys wouldn't have tolerated), a variety of talking heads - including the ageless Billy Bragg - discuss the sisters' rise to prominence: the coup is Kiwi PM Helen Clark, lauding the fashion in which the sisters brought to mainstream notice (and thus "made acceptable") gay and lesbian issues ahead of a key social reform bill. The Topps' own characters - two dirty, chainsmoking old men (an homage to long-time Dame Edna support Les Patterson, maybe?); a pair of theatre-camp directors obsessed with etiquette and mildly blue jokes; and a toothy twosome parodying the purveyors of the drippy country songs the Topps have no truck with - also appear to comment on the phenomenon, adding to the sense of fun. Yet nothing is allowed to obscure the sisters' cultural significance, both within New Zealand, a place where lesbians (as per Heavenly Creatures, say) had previously been understood as "women who murdered, women who were murdered, or women who committed suicide", and within the ultra-masculine world of C&W; but then again, what's this musical genre all about if not girls who - like the proud, defiant mares pushing against the fences in the Topps' top field - simply refuse to be tamed?

The Topp Girls: Untouchable Girls opens in selected cinemas from tomorrow.