Tim Dowling: have you heard the one about the out-of-tune banjo? My banjo, to be exact

The band I’m in is in the middle of its autumn tour: Hertford, Stroud, Nottingham, Scunthorpe. On the first night, in Oxford, we play in a big church, where I make a conscious decision to censor the profanity of certain lyrics, then forget all about it and leave the F-word ringing against the old stone columns.

On the second night we’re in the theatre of a specialist music school. Everywhere we go backstage we hear instruments being played brilliantly on the other side of the walls: piano, drums, trumpet.

“It’s a bit worrying,” says the bass player. “These people all know how music is supposed to sound.”

“They don’t seem to have a banjo programme here,” I say. “Which is lucky.”

In the second set, the fifth song begins with a new arrangement: a sonorous drone provided by the keyboard player which is meant to set the atmosphere. Unfortunately I am obliged to tune my banjo while it’s going on.

“Don’t worry,” I tell the audience. “This is part of it.”

For the third gig of the tour we head to Cornwall to play at Carnglaze Caverns. Ahead of our arrival I have managed to glean only one fact about the place: it’s a cave. I imagine this means that the venue is some kind of cellar, or a building taking advantage of a natural dent in the landscape, perhaps with a craggy back wall.

But what it actually means is: it’s a cave. Or more specifically, an old slate quarry hollowed into vast underground vaults by centuries of digging, 150 metres back into the hillside, with the stage at the far end. There’s a golf buggy available to drive our stuff into the cave, and a big box of hard hats sitting in front of the cafe outside.

“Do I have to wear one of these?” I say.

“Not while we’re playing, apparently,” says the drummer.

There is surprisingly little echo in the cave – due, they say, to the chisel marks covering every vaulted surface – but the venue presents other challenges. It’s a constant 10C inside, and humid. My glasses fog over and stay that way. My banjo, when I pick it up, is slippery to the touch.

Our dressing room is actually the front room of a bungalow – by the cave mouth – where the cavern’s owners Tony and Lisa live. The rest of the band are warming up their instruments, but I’ve left my banjo in the cave because I was worried it would be impossible to tune after a journey from a damp 10C to a dry 21C, and back again. The fiddle player comes into the room and looks at me.

“Your wife is here,” he says, in a tone intended to convey mild alarm.

“Uh-oh,” I say. I go outside to find her dripping in a steady rain.

“I got so lost,” she says.

“Come into the dressing room,” I say. “It’s a house.”

By show time the rain has let up. There is, of course, only one way to the stage from the cave’s entrance: through the audience, up the central aisle. We decided to play ourselves in, like a marching band, but because I’ve left my banjo onstage I’m obliged to walk behind everyone with my hands in my pockets, like an old uncle who for unspecified reasons can’t be left unaccompanied. My banjo, when I get to it, is slimy, but in tune.

Playing in the cavern is frankly amazing – the lighting is dramatic, the acoustics are incredible and the audience can hardly believe their surroundings. By the sixth song of the second set, however, the humidity is taking its toll on the banjo. By the time I’ve tuned the last string, the first one is out again. This is not the first time this has happened; we have a contingency plan, which consists of a well-rehearsed anti-banjo monologue which the guitar player has already launched in to, and which finishes with a joke written on a piece of paper sitting in my breast pocket.

The whole set up works as it should – we reach the punchline just as the banjo finally holds its tuning. Then the guitar announces the name of the next song, and my stomach drops.

“Wait, what?” I say. The room falls silent.

“Have you tuned up for the wrong song?” the guitar player says.

“I don’t even play the banjo on this one,” I say.

As I walk to the back of the stage to exchange my banjo for a guitar – a guitar which I will soon discover is also out of tune – I have time to reflect on the difference between an audience of several hundred people laughing with you, and laughing at you. The difference, I realise, lies chiefly in forgetting to say: this is part of it.