Budding scriptwriters take note:

this story has a near-perfect narrative arc, a mailroom-boy-to-company-president sort of thing. It begins somewhere outside the big cities, takes 15 years in the telling and features three leading men supported by a cast of thousands. To give it the epic scale it deserves, you'd need to hop from place to place across the globe; for our purposes, however, we'll stick to a single location.

It's a story that should be told in chronological order to properly convey its rags-to-riches dimensions, but let's start near the end, then do one of those clever flashbacks things.

We're in the Ubiquitous Chip in Glasgow's Ashton Lane. At tables nearby, students and their happy families are celebrating after graduation ceremonies. They don't notice, in a far corner, one local journalist and two internationally feted rock stars.

One of the musicians has his long hair gathered up in a band so that the nape of his neck is bare to the world. He's sporting multiple tattoos and a beard that would be termed "hipster" had he not foreshadowed this current trend years in advance. This is Simon Neil, guitarist and singer with Biffy Clyro.

Beside him, quieter but no less funny, is a slighter figure, his hair and beard a gingery blond, the tattoos on his arms an almost pale green. This is James Johnstone, bass player with Biffy Clyro. His twin brother Ben, the band's drummer, sits this scene out.

The dialogue on the soundtrack grows louder, and it becomes apparent that they're talking about T in the Park, about how Biffy Clyro will headline the Main Stage on Friday July 11, and about how this marks the tenth time the band have played Scotland's biggest summer music festival.

"We just want T this year to be one of the best nights of our lives - and one of the best nights of everyone there's lives too," says Simon. "That's what we try to achieve every night, it's what keeps us going. Sometimes it can be tiring, touring and playing shows all the time, but you've got to have that belief every night - that you can transcend something, transcend the moment."

"We want to feel we can do better every single time," agrees James, noting that news has just filtered through that, after 18 years, the festival will be moving across Perthshire from Kinross to the Strathallan Castle estate for 2015. "It's quite fitting that it's the last year it'll be in Balado. It's a nice way to round off where we've come to as a band."

"Because," says Simon, "our journey has been all Balado, hasn't it? I think we know every square foot of that site, from the good times and the bad. From crawling along the floor, trying to find our way home, to running about with a guitar, trying to play. There's something nice about us headlining, if it's going to be the last year…"

FLASHBACK: PRE-TITLES SEQUENCE

It's 1997, and Biffy Clyro have risen from the ashes of an earlier band formed in an Ayrshire school. At this point, Simon, James and Ben are studying at university and college in Glasgow, but their teen years in their chosen musical genre haven't been easy.

SIMON: We're from Ayr and Kilmarnock, so every time you met someone who saw you played music, it was that parochial 'Oh aye, with your stupid long hair… Rockers? Losers!'

JAMES: You learned to be either a good fighter or a fast runner, growing up with long hair in those towns. I think we ended up being fast runners…

SIMON: … a few times belting up Glasgow Road in Killie, going 'Oh f***!'

SCENE 1: T BREAK STAGE, 1999

After successfully competing in the live heats at King Tut's, Biffy Clyro are chosen to play the unsigned T Break stage at T in the Park. It's the first time the three of them have been to the festival together and it's a real rites-of-passage moment: all three band members are 19 years old

SIMON: We drove ourselves up in a camper van. Actually, James still has a Volkswagon camper van, but the very first one he had took us all round the country, and that was one of our first trips.

JAMES: We left the drum kit set up in the back. We thought it would be easier than taking all the cymbals off the stands…

SIMON: So as we drove there, we were standing against the walls, trying to not let the drums go… Our passes were very much only for the Unsigned Tent as it then was, but we somehow ended up in our van behind the Main Stage as Faithless were playing. This was when Faithless were at their height and there were 30,000 folk just bouncing… and at our gig there was maybe about 30.

JAMES: We played hard and, I think, we really played well.

SIMON: I'm sure that's when we saw Mogwai. It was one of those moments when you realised here's a Scottish band headlining a stage at a festival [Mogwai headlined the King Tut's Tent on the Saturday while Blur were on the Main Stage]. Apart from the fact it was one of the best shows we'd ever seen, it was just one of those moments. 'This is brilliant. Here's five kind of neddy guys from Glasgow making this weird music, and they're headlining a stage.' And it changed our lives, opened up possibilities musically for us.

SCENE 2: T BREAK STAGE, 2000

Exactly one year later, with independently released single Iname and EP thekidswhopoptodaywillrocktomorrow under their belt, Biffy Clyro are asked back to T in the Park, this time with an offer to play the same T Break stage alongside the bands who got through in that year's competition. It is a mixed blessing.

SIMON: That was one of our worst shows ever. Ben's drums broke on the very first beat of the bar of the very first song - we opened with a song called 57, where we all come in together. Ben's drums broke, I burst all my fingers open, they were bleeding and I could hardly play. My plectrum was sticking to my fingers because of the blood, and all the strings were going 'bleh-bleh-bleh-bleh'. Excitement got the better of us so that we ended up finishing that show thinking -

JAMES: - we'd blown it -

SIMON: - we should have been better this year than last. But we ended up getting a call a week later saying 'Roger Trust, the A&R guy [from the Beggars Banquet label] saw you and we'd like to sign you'. What the f***! I think he liked the fact that through the challenges that arose, we had played quite a good show. But we just saw the mistakes.

SCENE 3: MAIN STAGE, 2003

After rising up in size to Stage 2 in 2001 and the NME Stage in 2002, Biffy Clyro mark five years in a row at T in the Park with their first appearance on the Main Stage in 2003. Signed to Beggars Banquet, they have now released two albums: Blackened Sky and The Vertigo Of Bliss. The latter squeaks into the UK Top 50 at No 48.

SIMON: We deliberately made our first three records with obstinate songs and really complex stuff. We weren't inviting people in at that point. We hadn't quite appreciated the engagement that's required, and also that a show is as much about the people there as it is about a band. So we went on and played our most abrasive songs. And we were on before The Proclaimers.

I remember ending the 25-minute set on top of Ben - this is during the day at about 12.30pm - screaming my lungs out, as I'd probably dropped the mike. And it was on the telly, bizarrely, and I remember watching, thinking it was a lot of fun but what were people meant to get out of that? It's just three angry guys getting f***ing mad.

JAMES: We were sort of doing what we were doing at King Tut's - but on the Main Stage at T in the Park. When you look at Nirvana at Reading, there's not much showmanship going on and the sound was terrible, but it had heart and soul to it. I think that's what engaged us more than playing perfectly or all that 'You guys having a good time?' stuff. The spirit and the passion. But later you start to realise that the audience are more important than the band in some ways. If you don't deliver something that they're going to enjoy, then you're rubbish. Forget it.

FAST MONTAGE: MAIN STAGE, 2005; RADIO 1/NME STAGE, 2007

SIMON: I remember I was line-checking my guitar [in 2005], and Pete Townshend walked past. He was playing with his girlfriend at that time, Rachel Fuller, and he wouldn't stop moaning about the volume of my guitar. I mean, Pete Townshend! A couple of years later, we played with The Who and they put in an official complaint about the volume of our music because obviously Roger Daltry has really bad ears now too and is pro-ear protection. Something doesn't sit right in my mind about The Who telling us to shut the f*** up.

SCENE 4: MAIN STAGE, 2008

After a third album on Beggars Banquet - Infinity Land - the band sign to Warner Music offshoot 14th Floor in 2006. Major label backing has an instant effect: new album Puzzle reaches No 2 in the first week of its release and the singles Saturday Superhouse, Living Is A Problem Because Everything Dies and Folding Stars all go Top 20.

SIMON: That was the first album where we really focused on the songs, let the lyrics take hold, and there was a bit more space in the music. I think it was the first year we had songs that were even compatible with a festival; 2008 was the start of that inner confidence, the belief in our band, that we were worth being in these positions and we were worth people coming to see us.

JAMES: It had almost been like trying to choose your fans. If they weren't cool little rock kids, then they didn't understand our band - that's how we'd felt. 'You're not weird enough to like our band.' And eventually you realise that's a stupid opinion to have and it should be more open than that.

SIMON: The album Puzzle was about my mum passing away, and we had a tough few years, but the music kind of opened a door to us. It was the first time we let people in, and I think that people then embraced the songs because there was finally a glimpse of who we were as people.

SCENE 5: MAIN STAGE, 2014

And so we reach the story's climax: Biffy Clyro come full circle, from unsigned band in 1999 to Main Stage festival headliners in 2014. In the four years between playing the Main Stage in 2010 and now, they enjoy their first No 1 album with Opposites. They also see their song Many Of Horror become the 2010 Christmas No 1 in the shape of X Factor winner Matt Cardle's cover version, When We Collide.

As T in the Park approaches, they play the PinkPop festival in Holland, on a bill that sets them alongside fellow heavyweights Avenge Sevenfold, Metallica, Rob Zombie and Mastodon. A few days later, they headline the Isle of Wight, this time beside the likes of Rudimental, Tom Odell, Calvin Harris and Katy B, knowing there aren't many bands in the world who could triumph in front of such a diverse set of crowds.

SIMON: At a festival you have to have songs that people know and that matter to them - that's what a festival headliner is. And that's what comes from radio and stuff like that. We still try to play at least one song from each record because, to us, every album is as important. And because it's T, I think it's important we do play songs that represent every era of when we've done the festival. But as much as we'd like to, we won't go out and play a new song. There's a time and a place to bleed in something new, and I don't think a festival is that place. A festival is about joy, it's about community.

JAMES: This last year, we've been having more fun. There's no need to beat yourself up beforehand, and that's much more enjoyable.

SIMON: The first few times we got to play on the Main Stage, it felt like because we were a Scottish band we got a help. But when it reaches this point with Paolo Nutini and Calvin Harris, it's because of who they are and what they've done. It's nothing to do with the fact that the festival is in Scotland: these guys are headlining festivals all over the world. Scotland's in a real strong shape at the moment.

SCENE 6: THE FUTURE

It's early days in the writing of Biffy Clyro's next album. However, as they did with the 18-track B-sides album Lonely Revolutions that followed 2009's Only Revolutions, this summer they'll be releasing another B-sides collection, featuring 16 tracks, called Similarities.

SIMON: Every time we make a record, I like to clear the decks and not have any songs left over because I think the next album always needs to start from scratch. It's a shame these songs [on Similarities] didn't make it onto Opposites. Some of them were very close. To me it completes a picture. I'm reticent to go into details about the next album, but we're moving on to new stuff and part of that is getting Similarities out.

CHEEKY WEE POST-FINAL CREDITS SCENE

It's only a parting throwaway joke from the journalist to the rock stars. Next year, T in the Park leaves Balado and moves to a new site. It's the start of a new era. And so, guys, have a look at your B-sides albums, make up a set list that most audiences won't recognise, invent a new name for your band, enter the T Break competition, play until your drums break and your fingers bleed. And a new cycle, a new story, begins…

SIMON: I don't know if we've got another 15 years in us.

Biffy Clyro headline the Main Stage at T in the Park on Friday July 11, www.tinthepark.com

Similarities was released by 14th Floor/Warner Music on 24 June.

DELETED SCENE

During the interview, the journalist asks if there are any new bands on this year's T Break line-up that Biffy Clyro think might go far. They admit that, touring abroad as they do, they're not as up on the grassroots scene as they'd like to be. A mere 36 hours later, the journalist gets a text from the band's manager: James has gone through the 2014 T Break list and noted down some words of support.

JAMES: I had a listen to the T Break bands... and I'm totally blown away. The future of music in Scotland is in safe hands! There is such great diversity amongst the groups and a huge amount of talent on show. It feels somehow unfair to single out only a few bands as it truly feels like they all deserve a mention, but I'm sure in the future they'll all get the attention they deserve.

My personal favourites were Deathcats, with some pretty great noise and a f***-you attitude. The wonderful Model Aeroplanes clearly have a great future ahead of them. It's great to hear such young guys producing such perfectly crafted songs and I'm sure we'll hear more from them. Birdhead have a really eerie lo-fi sound and they're a classic example of how repetition can be a good thing, but only if you do it for long enough!