I keep going outside big television studios and shouting into a megaphone; it’s a thing I do when I am not writing this column. The BBC really wants me to stop. ITV, frankly, quite likes the attention. But what I always say into my military-grade amplifier is this: there is no substitute for chemistry.

I’ve made this my hobby because, wow, the television I have had to endure over the past few years where guests can barely open their eyes in front of presenters, or actors can barely bring themselves to pretend to like each other, or basically every Richard Ayoade episode of . If the people on screen don’t have any chemistry with each other then you are wasting an hour of my life. If I want to watch small talk fail on the vine, I can go to a party and do it myself!

Apparently, whoever is on reception at Channel 4 has been passing my scrawled letters upstairs, though, because this week they are giving us the delightfully charming one-off gift of Dame Judi and Jay: The Odd Couple (18 August, 9pm, Channel 4), an hour of television that will go down as one of the year’s weirdest crossover events but also one of its most soul-enriching.

The pitch is this: Jay Blades from is best mates with Dame Judi Dench, right? Did you know this? They, like, actually are. They met on an episode of The Repair Shop – the BBC’s most regular make-you-well-up wholesome television franchise and also, in my opinion, one of the most unmissable Christmas specials around – about two years ago and now they just, like, hang out. I know, it’s wild isn’t it? Dame Judi is 89 and got an OBE the year Jay Blades was born. Jay Blades wanted to be a DJ before he became Britain’s most prominent flat cap-wearer. He has a gold tooth and she has astonishingly blue eyes. Their height difference is completely bananas. But somehow, it works. And it makes for magical television.

The crux of the show isn’t going to change your life: they go on a five-day road trip, and when I say road trip I mean “three places in London and one a little bit outside London”, and show each other little episodes from their past. Jay takes Dame Judi to Ridley Road Market and she somehow ends up manning a plantain stall. Dame Judi takes Jay to the Old Vic and performs some startlingly good Shakespeare to an audience of one.

They walk arm in arm, they potter along canals, they drive around in an Aston Martin that Dame Judi looks absolutely miniature in. They ramp up the “odd couple” stuff just the right amount to make it obvious that they are very different people but to also play up the real friendship.

Dame Judi keeps tossing pesky little one-liners away to the camera. “What’s the major difference between you two, do you think?” a producer asks, out of shot. “He’s very tall,” she twinkles.

But it’s the true warmth between them that makes this show such a pleasant hour of television (I am one of the most miserable and cynical people I know, and I watched the whole thing with a broad, dumb smile on my face). “Road trip TV” has become a big thing in recent years, and sometimes odd couples going somewhere and doing something is great () and sometimes it’s excruciating (anything Sky makes with Jamie Redknapp).

Most often, though, these shows creak at the seams – you can just see how much every set piece has been planned to the tiniest detail, inventoried and scheduled to death, every filming permit sucking a little bit more life out of the eventual show. But Dame Judi and Jay never succumbs to that; they truly delight in each other’s company – she’s a wicked little imp and he’s the kindest man alive – and they love hanging out with each other and I love hanging out with them, too.

There are so many gorgeous moments that fill the hour – learning that Dame Judi has a joke 007-themed doormat being one of them – and then something phenomenally weird happens, such as Jay Blades teaching Dame Judi how to mix white-label jungle vinyl, which she does while wearing a long, elegant silk scarf. The more I try to explain it, the weirder it sounds. But this show is as mindbending as it is heartwarming. Give me 100 more episodes of it, please. There! Is! No! Substitute! For chemistry!