The best pop groups want to change the world. They want to leave an imprint that no one forgets, to do more than check out as a minor statistic in the Guinness Book of Hit Singles. They want to change the world of pop, and to engage with the politics of pop. Belle & Sebastian have re-invented the pop festival; they signed to a tiny independent label but still beat Steps to a BRIT, before sweeping into the Top 40, then the Top 20. They've brought their lost sixties heroine, Evie Sands, over to play a show in Glasgow. They've sold out a concert at the Hollywood Bowl. And, in 2014, they've cut an album - their ninth - called Girls in Peacetime Want to Dance, that blends electro-glide, baroque balladry, and giant-sized Europop hooks. They deserve several accolades, each of which are rare for any band in 2014 - Belle & Sebastian are unique, unpredictable, and fiercely loved.

Part of their appeal is that Belle and Sebastian have always given the impression of being completely unaware that they are even famous. Emerging in the late nineties, they appeared to be both press and camera-shy, but also entirely self-contained; they seemed to have a secret, something built around books and films, and yet were happy to share the love, stopping just short of writing individual songs for their fans. And their fans, naturally, became obsessive, formed their own bands, started their own loosely affiliated clubs, radio shows and websites. A secret gang - who wouldn't want to be a part of it?

But then again if you're a band who works with Trevor Horn, Carey Mulligan and Norah Jones, you're probably not content to lurk in the tiny shadow offered by a seven-inch single on Postcard. And if you end up on the soundtrack to Adam Curtis's The Power Of Nightmares, or Todd Solondz's Storytelling, as well as Juno, then there's going to be more than a little grit and grain to your music than adjectives like "shy" and "fragile" might suggest.

Belle & Sebastian have always understood well the art of song structure. They write precise and elegantly constructed melodies, and have never skimped with middle eights, bridges and codas: check ‘Perfect Couples’ on the new album, with its unexpected northern soul stomp right at the tail-end. Stuart Murdoch's character studies and pen portraits deal in suburban dreams and anxieties, nudge-nudge innuendo and gentle mockery, real hope and real tragedies unfolding in offices, shops, libraries. It's an uncommon talent that can manage this, and also be very funny.

Murdoch's lyrics have very rarely been first person - at least, they haven't until now. ‘The State I Am In’ opened their account in 1996 - Tigermilk, side one, track one - a tall story about a fictional life, all moonshine and myth, fictional novels and maybe the life story Stuart Murdoch wanted for himself as he lay in his bedroom. The opening track on Girls in Peacetime is no shaggy-dog story, it IS Murdoch's life, at least the life he led just before Belle & Sebastianwas born. Stuart Murdoch was housebound with chronic fatigue syndrome prior to the formation of the group - it's a period he has drawn on before, but never has he written anything as direct as ‘Nobody's Empire’ - side one, track one of the new album. He says it's the most personal thing he's ever written - Belle & Sebastian have never sounded as open.

Girls in Peacetime is also their most sonically diverse album: there's the klezmer chorus on stand-out track ‘The Everlasting Muse’, radio anthem ‘The Party Line’ with its Chic guitar and filtered-house intro, and the squelchy synth break on ‘The Book Of You’. It ends with the bleached-out, solarized beauty of ‘Today (This Army's For Peace)’, with a woozy 1968 feel, somewhere between the Monkees' ‘As We Go Along’ and Robert Wyatt: "Come out into the light, today." They have worked with outside producers ever since Trevor Horn helmed Dear Catastrophe Waitress in 2003, plumping up their sound, pumping it full of light and air, and getting ‘Step Into My Office Baby’ unlikely but welcome repeated plays from Ken Bruce on BBC Radio 2. This suggested a sharp step away from the tape-swapping, pen pal world they had been thought to inhabit (of course they never had, not really). Tony Hoffer (Beck, Air, Phoenix) was hired for The Life Pursuit (2006) and Write About Love (2010). The new album was recorded in Atlanta with Ben Allen (Deerhunter, Washed Out, CeeLo Green and Animal Collective) who convinced them to leave things more open-ended, less thoroughly thought-out in advance, leaving the producer and the musicians more space to be spontaneous. The result is playful, super-melodic, with lyrical nods to both their past and an optimistic future, and joyful jumps into new musical territories.

Belle & Sebastian have stood as something different right from the beginning. Let's have a quick poke around the previous eighteen years. Debut album Tigermilk (1996) was the product of a Stow College music business class that drummer Richard Colburn was taking; just 1,000 vinyl copies were pressed. In spite of huge major label interest (immortalised on the track Seymour Stein on their third album, The Boy With The Arab Strap) they initially signed to the tiny Jeepster label, then later to Rough Trade and now have their first worldwide deal with Matador Records. The key to their appeal was a sense of community. Their self-curated Bowlie festival would evolve into All Tomorrow's Parties; they became central to a nascent message board culture, and a US loop of labels and fanzines (even writing a song about one, Chickfactor) that adored their music, their stance, and their imagery.

In Britain they famously upset the applecart in 1999 by winning the "Best Newcomers" BRIT award through the votes of their fans, faced accusations of vote rigging, and in the process have got the backs of the tabloids up (sample Daily Record headline: "Belle Boy's At It Again"). So, clearly, they've been doing something right.

There's nothing obviously tabloid-baiting on Girls in Peacetime Want to Dance, though the bold step onto the dancefloor is bound to raise some eyebrows. "Be popular - play pop, and you will win my love" is the final line on ‘The Everlasting Muse’, and is the lyrical heart of an album about love, the love of music, and the power of pop. Given that Murdoch has openly declared himself pro-bubblegum before, it shouldn't come as a surprise that ‘Enter Sylvia Plath’, ‘The Book Of You’ and ‘Play For Today’ have keyboard hooks that recall Scandinavian pop machines past and present. The filmic loves, kitchen sink imagery and baroque touches are still there, too, don't worry.

It's all about trusting in the restorative power of pop music. If you'd trust anyone to write a great Europop song about Sylvia Plath, you'd trust Belle & Sebastian.

- Bob Stanley, October 2014