Don't go looking for a setlist at Nick Harper's gig - there won't be one.
In fact the singer songwriter son of Roy is unconventional in many ways, from his idiosyncratic guitar tunings to his ad lib concerts where anything goes:
"I play whatever comes into my head at the time or whatever someone shouts out, I just get on with it," says Nick.
"All my songs are acoustic guitar based and voiced, there's never been a band rehearsal thing, it's always been me on my own that's started it, so the foundation is there and I can play the song.
"What tends to happen at the start of a tour is I just play whatever comes and by halfway through the tour it's got into some sort of order.
"There's a rough map in my head of how to get to the end of the gig, but it can change at any point and every gig's different, but with this being a one-off gig it'll just be off the cuff - it's never been a slick commercial professional show... well maybe professional but it's always been a bloke stood in a room playing."
Since debut Light At The End Of The Kennel, Nick has built a fine following, whether solo, with band or accompanying dad Roy on tour.
Sadly this summer the partnership was disrupted when Nick broke his left arm. A break, if you'll pardon the unfortunate pun, of more than a month from his customised guitar.
"You that euphoric feeling you get when you've ill and you're back to normal operations, it was great," he says of his return to music.
"I was really pleased 'cos I hadn't been able to play at all for five weeks which is quite a long time for me... then all of a sudden I had to play - I broke myself in gently first couple of gigs, quite relaxed."
Any fans fascinated by musical minutiae will note Nick's guitar is unlike any other when he plays the Songwriters Festival:
"I use conventionalish tunings but there are a couple that are made up," he reveals.
"What really baffles most people is the staffing point which is a string down from a normal guitar it's like a baritone guitar, so the bass string is tuned to a low B and then D tuned to a low A..."
Hope you've all got that.
"I don't know if you know string gauges..." Nick adds. "...but I've got a 66 on the bottom which is like a piano string, so I've got shovels for fingertips but the guitar sounds massive."
So how did Nick come to have such a unique instrument?
"It was all a fluke really," he explains.
"I'd been playing with my dad and he's been playing so long his voice has gone down over the years and he's taken his guitar with his voice.
"So when I was playing with him, when I started 10, 12 years ago I tuned my guitar to his and steadily got lower and lower and the strings go floppier and floppier, more and more useless.
"As this was happening I was writing my songs and and there was no escape - in the end and I had to do it, so I butchered this guitar and it came out sounding wonderful!"
Nick's dad Roy is a well-known face and name on the circuit, having played with many of the greats including Jimmy Page, who paid tribute to him on Led Zeppelin III's track Hats Off To (Roy) Harper.
Was it inevitable, then, that Nick should follow in his father's footsteps?
"I'm all confused about skill and talent and the difference between the two, but I think it was inevitable," he admits.
"I had a ukulele when I was two - so I'm told - but I didn't learn any conventional music until I was ten, first three chords.
"My parents were fantastic, always supportive but I wanted to play music," he adds.
"My major contact with my dad when he was on the road was through his records, and I think I thought that was maybe what grown-up Harpers did, play music."
Next year will be a busy one for Harper Jr. A live album in progress, Nick also plans to release a new studio record, songs from which will get an airing at Ronnie's:
"It's the hardest test and the most instructive to play in front of people but when the songs aren't finshed and polished it's probably also the most nerve-wracking and edgy way of introducing them to the world," Nick says.
"If you've written a bunch of crap you soon know it!"
