In the early days of T in the Park, way back in 1997, a Glasgow-based indie band played the T Break New Talent stage to a modest crowd.

They were loud and melodic and their influence still noises up Scottish pop. They were called Lungleg.

There were a few other notable artists on 1997's T Break stage - not least an alt-rock troupe called Polar Bear, who would later change their moniker to Snow Patrol and shift millions of records. Theirs is a familiar T Break narrative: the indie-rock odyssey from local unsigned tent to global arena, as perpetuated by the likes of Biffy Clyro, Twin Atlantic, Frightened Rabbit and Travis (who played as Glass Onion in 1994 when the T Break stage went under the Caledonia banner).

With the continuing sponsorship of Tennent's Lager, T Break was set up in 1996 to spotlight unsigned talent at T in the Park, and it continues to have a place in the hearts of the artists who have played it. "Because T in the Park was such a huge festival, and it wasn't commonly done for a young band like us from a small town, [T-Break] felt like our only opportunity to get our foot in the door," says Biffy Clyro guitarist and vocalist Simon Neil. "It was the only opportunity to play to people who wouldn't know our band." The band's bassist, James Johnston, agrees: "I think T has always been good at ... helping support local bands like us."

Yet as T Break celebrates its 20th year, and announces its class of 2015 (see panel), what strikes is that its line-ups over the past two decades don't just feature some stadium-sized success stories like Biffy's: they also tell a tale of the underground - of DIY labels and musical evolutions and the ways in which counterculture has long shaped (and upturned) our Scottish pop landscape.

Lungleg are a case in point. In the mid-1990s, the femme-punk four-piece were at the forefront of a thriving local grassroots scene that also gave rise to the likes of Club Beatroot (RM Hubbert, Mogwai, Franz Ferdinand via The Yummy Fur) and Chemikal Undergound (Bis, Delgados, Arab Strap). Lungleg's rock 'n' roll stramash of indie pop and riot grrrl can be discerned in Scottish bands since, from Sons And Daughters through Honeyblood (who played T Break in 2013) to The Van T's (who play T Break this year). When Franz Ferdinand recently played a live session for Vic Galloway on BBC Radio Scotland, they covered Lungleg's Maid To Minx.

The Lungleg tale is not unique: cast an eye over T Break's previous line-ups, and witness the myriad subcultures and genres that make our music scene so exciting and ingenious - from Ghanaian hip-hop (Kobi Onyame, 2010) to vintage rockabilly (The Kaisers, 1997); from kosmische folk (FOUND, 2011) to sublime electronica (Conquering Animal Sound, 2011); from deviant blues-punk (Uncle John and Whitelock, 2004) through legendary cult-pop (Life Without Buildings, 2001) and neo-classical metal (Lapsus Linguae, 2001).

You can also chart the evolution of many of our best-loved bands, from their nascent roots to the present day. Admiral Fallow played in their erstwhile guise, Brother Louis Collective, in 2009; electro-prog insurgents Multiplies (2005) spawned Remember Remember and Errors, among others; shitdisco (2006) begat Ubre Blanca; Down The Tiny Steps (2007) gave us Jonnie Common; and Drive By Argument (2007) spawned members of Prides and Paws. Perhaps most impressive of all were Julia Thirteen (2002) whose bygone cast have gone on to play in Chvrches, The Unwinding Hours, The Twilight Sad, Bdy_Prts and many more.

Granted, T Break's history has also had its share of identikit indie, but the judging panel of industry figures who elect the 16 bands each year appear to actively seek out myriad subterranean sounds, as well as superstars-in-waiting. (Additional bands beyond the unsigned 16 who play the T Break tent are booked by promoters DF concerts). The addition of Louie from Hector Bizerk to this year's judging panel has done no harm to its credibility, either: the Glasgow hip-hop livewire is a vocal proponent of gender equality, DIY activism and shining a light on the underground. And as one 2013's stand-out T Break bands (along with Honeyblood), he's also one of its success stories.

Louie's T Break judging experience casts some light on the thought processes, and democracy, that are at play behind the scenes. "I know that every single time the T Break line up's announced, there's a bitterness with bands that don't get picked - people are always looking for conspiracy theories," he says. "But when we were picked to play T in the Park two years ago, I had never met a single one of the judges. I think it's important for bands and artists that apply to T Break to know that - that it's not some jobs-for-the-boys closed group, or anything like that. It's the most open discussion that you could have about over a thousand bands getting whittled down to 16. It's purely 'Should this band be considered or not?'"

Some decisions this year were self-evident, says Louie. "There were some bands where it just felt like the right time for them," he says. "Tijuana Bibles, of course - those guys will fill that tent, they're on an upswing, they've been out touring, they're working really hard, they've got a new record coming out, just everything. It ticks every single box, and they should absolutely be there this year. Gerry Cinnamon was one that was an almost unanimous decision as well. He's got a crowd pull and charisma that will shine through at T in the Park. That tent will be mental when he's playing; I think the whole of Castlemilk will be there," he laughs. "So we really did consider a lot of that - where the band are in their crowd-pulling, what stage they're at - not just the music on its own."

For other acts, the element of surprise is key: they're maybe still under-the-radar, but have the potential to knock crowds for six all the same. "Spring Break are a hip-hop band from Dingwall," offers Louie. "I've known one of them for years so I vetoed my vote on them, but it was pretty much a unanimous verdict, even though they're very much in their infancy. There were comparisons with Jurassic 5 and De La Soul, and people were commenting on the fact that it's not often we get something like that from Scotland - that kind of summer feel."

Louie's tales of T Break judging also cast light on some of the reasons an artist may not be selected for the T Break stage, even if they're relatively established: T in the Park's party clamour is not suited to everyone. "I wanted to make sure that I wasn't just voting for acts because I like their music," he says. "I voted for acts I thought would be suitable for T in the Park." He cites some excellent quieter acts and makes the valid point that their charms would be lost in a rowdy festival environment. "We took that into consideration too," he says. "Would this actually have an adverse effect on the artist? In some cases, it does. It can actually be off-putting."

He also says, in hindsight, that even Hector Bizerk may have played a bit too early; that they'd have pulled more of a punch (and reaped more reward) from playing in 2014, or even this year (sadly, they're not - yet - on this year's TITP bill). But he's nonetheless delighted that Hector Bizerk made it through to T Break in 2013. "It's every Scottish musician's dream to play at T in the Park, I think," he says. "It's the biggest and best festival, and the media attention that you get from playing at T Break is amazing."

He also notes that T Break offers a vital platform for grassroots acts - across myriad genres - as well as those with the potential to break through to the mainstream. "For most bands, when you're at a level where you're applying to play at something like T Break, you don't have a marketing budget, you don't have a big team behind you, you don't have an agent who's going to use their muscle to get you onto a festival like that," he says.

Then he echoes the words of Biffy Clyro: "Playing T Break is a genuine accolade. And the beautiful thing is that it makes T in the Park reachable for people like us."

T in the Park takes place at Strathallan Castle, Perthshire, July 10-12. See for line-up and ticket details. For more about this year's T Break bands, go to