So what have we learned today? How to make a comedy gameshow enjoyed by millions

Taskmaster is about to air its 20th UK series and has spawned versions all over the world. Rachael Healy discovers its secret

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Outside some nondescript gates in west London, a lone fan has arrived from overseas, hoping to catch a glimpse of the oddly shaped house that lies beyond. This is a common occurrence, the film crew working there say.

The former groundskeeper's cottage is the Taskmaster house, the setting of the comedy gameshow that has been watched by tens of millions of people in the past decade.

The team is back on set to film the show's 21st series, with the 20th run due to be released in the next few weeks. The concept is simple: five comedians compete across 10 episodes in various baffling tasks (one of the originals was: “Paint the best picture of a horse while riding a horse”), then reunite on stage to watch the results and face judgment from the Taskmaster himself, Greg Davies.

It is one of British TV's biggest success stories. The show's creator, Alex Horne, devised the concept as an Edinburgh festival fringe show 15 years ago, and initially struggled to find a broadcaster to take it on.

Now it’s an irrepressible machine, spawning versions in Australia, Canada, New Zealand, Belgium, Spain, Sweden and Portugal, plus spin-offs such as Junior Taskmaster, hosted by Rose Matafeo, who finished second in series nine of the original show. There have even been live summer experiences at English Heritage sites where fans can become contestants.