Anyone with a freeview box or a few extra digital channels will have stumbled across Dave, which seems to have about three shows on rotation, including a unique and greatly-missed improvised comedy show, Whose Line Is It Anyway?

Presented by Clive Anderson and starring some incredible comics such as Paul Merton, Stephen Fry, Ryan Stiles, Mike McShane, Josie Lawrence and Jim Sweeney, it is about the only reference point most people have to improv.

But it all started with the Comedy Store Players, who began performing scriptless comedy nights at the Comedy Store, Piccadilly, in 1985, and went on to supply many of the comics that starred in Whose Line.

One of the originals who made the step up onto TV was Richard Vranch, who was the musical accompanist on the TV show, but was one of the original stage Players. And this weekend, the legendary Comedy Store Players comes to the Cannizaro Park Festival in Wimbledon.

And Richard explains why there is no substitute to witnessing it in real life: "You just have to be there - it is better being a participant than just watching a porn film! You are part of the contract because you can shout out suggestions and watch them happen there and then.

"It's the old cliche about the crowd being the 12th member of the football team. Essentially, it's a live thing. Doing it live is what we love and why we have done it regularlarly for 25 years."

Ingeniously, the Players treat the audience in the second half to a longer narrated scene, a whole story that is a world away from the snappy one-minute games and sketches you may be more used to.

But whether the game is long or short, Richard says that there are three golden rules to improvised comedy: l "Listen! It seems very obvious but it is so important and a lot of people simply don't listen. If you don't, you won't know what you can say next."

l "Try to move things along. You can be quite passive and that's fine, but the extra weird stuff happens when the writing and performing experience comes into play, and you can move the sketch along. It's like a jazz band which has been together a long time."

l "You really have to co-operate with the other people. It is weird that comedy comes in all different forms - it can be rude or political or benign, but ultimately there is a bedrock of co-operation which makes it satisfying to watch."

Abiding by these rules, and perhaps breaking one or two of them, on Sunday will be a star line-up of Richard, Josie Lawrence, Neil Mullarkey, Lee Simpson, Andy Smart and Mike McShane.

The Comedy Store Players, Cannizaro Park, Saturday, July 26, 8pm, £23/£25, call 0870 060 2512 or visit canniz aroparkfestival.co.uk for tickets.