Was Now That's What I Call Music! the first album you ever bought? That first Now set the template for the next three decades. It mixed chart-topping killer (Duran Duran, Culture Club) with also-ran filler (Limahl, Tracey Ullman). Credible acts (The Cure, Madness, Simple Minds) rubbed shoulders with novelty turns (Will Powers, Rock Steady Crew). This is the beauty of Now. It isn't artfully curated, it's democratically random. An un-retouched snapshot of the hit parade in all its eclectic, genre-hopping glory. Next Monday, a star-studded ITV documentary, The Story of Now, traces the history of the phenomenon on its 30th birthday. We hear how in the Seventies, the compilation market was dominated by Top of the Pops albums. Nothing to do with the BBC institution, these boasted scantily-clad models on their sleeves and featured all the hits of the day - except they weren't the original versions, but covers played by session musicians. Swizz! How Now got its name is a rather sweet story. Branson recalls hanging around a bric-a-brac shop near Virgin HQ on Portobello Road, just because he fancied a girl who worked there. Eventually he had to buy something and stumbled across a 1920s poster advertising Danish bacon. It depicted a chicken singing, while an enraptured pig declared: "Now that's what I call music." Branson bought it, hung it on the office wall and the rest is pop history. The pig became the mascot of the Now albums and Branson went on to marry the girl in the antiques shop, Joan Templeman, his wife to this day. Meanwhile, the Now series settled into a rhythm of three releases per year and grew from its humble roots to sell 100m albums - five times more than The Beatles and far outstripping most of the artists who've ever appeared on it. The film gives an intriguing glimpse into the politics of compiling. Record companies would only hand over their biggest hit if their lesser acts came as part of the package. Pole position on each album was track one, side one, meaning Queen and Paul McCartney fought over it in 1984. Madonna got in a huff when her True Blue album was kept off the top slot by Now 7 and refused to appear on subsequent compilations. Surprisingly for something so shamelessly mainstream, Now albums have become prized by collectors. The last vinyl, Now 35, is worth at least £50. CDs from the 80s can fetch up to £500. The franchise has found a zealous cult following, with Facebook groups, fan forums and YouTube channels dedicated to grainy VHS tapings of old TV ads. So what now for Now? Digital downloads were supposed to signal the death of the compilation. However, sales recently shot up for the first time in a decade and in 2012, 20.6 m were shifted in the UK. Faced with so much online choice, perhaps punters are rediscovering the convenient pleasures of compilations, now the fastest-growing sector of the digital album market. Naturally, Now continues to dominate, taking all four top places last year. There's life in the old pig yet. "The Story of Now" is on ITV on Monday, May 27 at 10.00pm