Whose Line (known as WLiiA to obsessive fans, who in turn are known as Whosers), is a kind of anti-gameshow. It has a host – but one with all the authority of a slightly befuddled supply teacher (with no discernable neck). Points are awarded – but with breezy indifference to what actually happens in each sublimely silly round.

The other special relationship

Forget the political "special relationship" between Britain and the States. Of far greater diplomatic importance is the special comedic relationship between the two nations that Whose Line has forged.

For, while the show began rather humbly on Radio 4, it began to attract US comedians like Ryan Stiles and Mike McShane soon after making the switch to telly. In fact, the American connection became so strong that later episodes were actually filmed Stateside. Eventually an American network decided to make its own version of the show, which to everyone's surprise was not rubbish. In fact, the US version enjoyed a sparkling run and attracted guest stars including Robin Williams, Whoopi Goldberg and – most marvellously – David Hasselhoff.

Wags and wits

The regulars on Whose Line comprise a veritable tapas bar of talent, bursting with spicy, garlicky gags and rich, oily innuendoes. And if you think that metaphor is rather laboured, prepare for Clive Anderson's elongated descriptions of everyone.

For example, Josie Lawrence is in Clive's words "the quick-thinking man's crumpet" while by contrast US comedian Mark Cohen is "the quick-thinking woman's filled bagel". Then there's Sandi Toksvig ("the Toulouse-Lautrec of the one liner") and Paul Merton ("the secret love child of Whistler's Mother and Van Gogh's Uncle").

And special mention must be made of Ryan's nickname – "neon love chicken" – which was earnt after he turned up wearing a calamitously bright orange shirt.

Game for a laugh

So many different games are featured in the series that it would be sheer folly (and incredibly tedious) to list them all. That said, it would be remiss of us not to mention the rounds which humiliate our contestants with admirable thoroughness.

Chief among these is "Helping Hands", in which one of them is forbidden from using their hands and must rely on a fellow contestant to stand behind them and lend their limbs for the duration of the game. Ryan Stiles is often the victim here, as the others seem to enjoy using this as an excuse to turn his mouth into an organic wastebin (his temporary hands have fed him cat food, sour milk and the soil from a potted plant).

Then there's the "Hoedown", in which the cringing, terrified players must come up with songs based on a subject suggested by the audience. Themes have included "making cheese" and "riding a pony" - the last of which inspired this Shakespearean-calibre couplet: "I was riding my donkey up a stony pass / I fell off, onto the grass"

The contestants tend to fear and loathe this round, and Colin often tries to get out of it by "fainting" or faking a heart attack (this is known as "pulling a Colin").

Stuff you might not know

While Whose Line is very definitely improvised (don't let the smug cynics tell you otherwise), many of the games are played a number of times so the contestants can offer variations, improve their gags and generally not look completely gormless. The best bits are then edited together for broadcast, so filming each episode actually takes several hours longer than the finished product.

Even more interestingly, the show has been adapted in a startlingly large number of countries. We've mentioned the US version already, but adaptations also exist in India (where it's called "Lo Kar Lo Baat"), Germanys ("Frau Schnauze"), Israel ("Shel Mi Hashura Hazot") and Belgium – which is the clear winner of the "unpronounceable alternative title" award with "Onvoorziene omstandigheden". Try saying that with a mouthful of jelly beans.