‘We heard from the back of the coach: ‘Help!’ And it was Biggins.” There may never be a greater line uttered on television, so praise be that Gone to Pot: American Road Trip (ITV) was ever thought up, and marvel that it came to pass. Although it promises to look at the legalisation of cannabis in the US through the eyes of Pam St Clement, Linda Robson, John Fashanu, Bobby George and Christopher Biggins, it turns into a comedic masterpiece and is by far the funniest thing I’ve seen on TV this year. It climaxes with panto legend Biggins and darts legend George vomiting furiously thanks to their overindulgence in a nonagenarian marijuana chef’s weed-flavoured ice-cream, on the back of a psychedelic bus in the car park of one of the most garish hotels in California. I’ll admit I was initially sceptical about the premise, but this is an instant classic. Gone to Pot for best-comedy Bafta. Heck, Gone to Pot for best-picture Oscar. It deserves them all.

A pot-smoking bus tour with Pat Butcher ... how did that show get made? Read more

It’s a fever dream of a documentary series that shouldn’t really exist. It’s a little bit The Real Marigold Hotel – and I wonder if this came from one hazy night, in which a producer type thought: “What else sounds like Marigold? Maritime? Mari ... juana?” – in that it packs off older celebrities on their travels, and even pinches George from series one. But to give it that necessary 2017 twist, it takes the premise of a very popular YouTube video, Grandmas Smoking Weed for the First Time, and adds it to the mix. The result is flamboyantly odd, or oddly flamboyant, and, aided by nothing stronger than a cup of tea, I was giggling from beginning to end.

Each of the five celebrities is coming at it from a slightly different place. The voiceover claims that they are all there with medical ailments, and wish to see if medical marijuana will help their mishmash of arthritic joints and mood swings. It is, we’re promised, a bid to see if legalising cannabis in the UK is a good idea. I love the notion that sending Pat Butcher and Christopher Biggins to San Francisco to paint a cactus while smoking bongs will somehow influence domestic drug policy. After watching this, I’m convinced that this bunch would be more capable of overseeing sensible legislation than the rabble currently in charge. But really, it’s all about watching five famous people getting stoned on camera.

Or not getting stoned, in the case of John Fashanu, who is intolerant of any drug-taking, ranks cannabis alongside heroin and cocaine, and declares that he is “high on life”. He seems petrified of trying it, although is eager to earn his place on the multicoloured fun bus transporting them around California. It’s hard not to hear him say, “If I take it, might I become extremely aggressive and start using martial arts? You don’t know, I’ve got 16 years. Four black belts,” without imagining Steve Coogan having written the lines, and you can’t fail to appreciate his imperious delivery of: “To debate it, I must know what it is like. So I built up enough courage to try the ice-cream.”

He does so at chef Nonna Marijuana’s house, tasting a bit of the pudding. Nothing happens. “Men are sometimes a little bit incautious,” notes St Clement, wryly, as a very smiley Biggins, who ate plenty of ice-cream, starts to sing My Way, forgets that he’s singing My Way, then loses the ability to speak. Four hours after dinner, in a sentence I cannot believe I am writing, Christopher Biggins and Bobby George are filmed whiteying on the bus.

It’s hard to pinpoint which bits of this documentary seemed most like an outtake from a long lost John Waters movie. It might have been the moment that George remembered he was missing three toes, then went behind the bar of his pub to bring one of them, preserved in vodka, to show to the cameras. It might have been when Fashanu was being massaged with CBD oil by an order of weed-smoking nuns called the Sisters of the Valley. It might even have been St Clement’s painting of the cactus, at an enterprise called Puff, Pass and Paint, which descended into what she declared was “the most incredible fit of giggles, which was thoroughly enjoyable”. Like Biggins with dessert, I gobbled the whole thing up.

Sadly, the preview clip for the next two episodes – the series is stretched out over a whole week, like a prestige Channel 4 drama directed by a Hollywood hotshot, as it should be – suggests our intrepid weed reporters will be forced to confront the darker side of the cannabis industry. I object in the strongest possible terms. There’s more than enough to enjoy in Robson evaluating hotel rooms (“It’s the Simon Bates Motel,” she says, of one dodgy inn) and St Clement having the time of her life. Let’s keep everyone’s spirits high.