Like all the best punchlines, nobody saw it coming. When a Cambridge Footlights troupe including Emma Thompson, Stephen Fry, Hugh Laurie and Tony Slattery won the inaugural Perrier award in 1981, comedy at the Edinburgh Fringe was a niche pursuit.

Since then the spectacular growth of comedy has been one of the defining characteristics of the world's largest arts festival and when this year's Fringe opens next weekend, comedy acts will outnumber theatre productions for the first time.

Comedy accounts for 32 per cent of the 2,088 shows at the Fringe this year with more than double the number of acts that appeared in 2000. Theatre makes up 29 per cent. It is a watershed moment in the festival's history.

Longstanding concerns that big-name stand-up comedy is swamping other art forms on the Fringe are particularly resonant this year. According to Nica Burns, one of the West End's leading theatre owners and producers, emerging theatre talent is increasingly gravitating to London fringe venues because it is cheaper than bankrolling an Edinburgh run.

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“Edinburgh really used to be the place where you could take a new play but now I think it's very, very hard to do it.”

Burns, who is also the director of the Intelligent Finance Comedy Awards (successor to the Perrier), said that comedy's emergence as the Fringe's dominant artform had become inevitable. It is also what promoters want. Theatre is more expensive to stage than comedy, where the costs are often just one performer and a microphone.

The credit crunch and a ticketing fiasco that left up to 150,000 festival-goers without their prebooked tickets as late as last week have raised fears that attendances will drop in 2008 after last year's record box-office haul.

If they do, the more obscure shows are expected to be the hardest hit. Edinburgh is still the place to go if you want to sit in a damp cave watching Latvian shadow puppetry while wondering whether to take a chance on that two-person musical about Christian fundamentalism.

This year's more unusual offerings include Dracula performed on a bouncy castle, a piece of experimental theatre inside a cage at Edinburgh Zoo and two shows in a swimming pool. Yet it is the comedians who lord it over the Fringe.

This year the fraternity has been split down the middle by the launch of a self-proclaimed Edinburgh Comedy Festival within the Fringe, hosted by the four largest venues. The Assembly Rooms, the Pleasance, the Underbelly and the Gilded Balloon say the festival can help them to pool costs and raise funds to invest in theatre and other art forms.

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