It’s December 2010. Hundreds of young demonstrators are kettled in Parliament Square by the Met’s scary territorial support group, despairing of the abolition of the education maintenance allowance, which kept underprivileged young people in colleges and sixth forms, and seeking to influence the parliamentary vote then under way on raising university tuition fees.

A makeshift PA system turns up, and the jack into the amplifier is passed around the demonstrators’ devices, all naturally loaded with MP3s. A rave erupts in the kettle, playing a huge variety of “music of black origin” – that unsatisfactory portmanteau word covering, at least that day, R&B, dancehall, UK funky and dubstep.

The place really goes nuts, though, when someone plays Pow! (Forward Riddim) by grime MC Lethal Bizzle. Long banned from clubs because of its ability to lay waste to a venue, this incendiary track has come to symbolise the frustration of young Londoners, many of them from council estates, and the suppression of their too fast, too threatening, too cold DIY music, snubbed by radio and effectively banned from live venues by police for years, until very recently.

Dan Hancox – an Observer and Guardian journalist and grime aficionado who writes about politics and pop culture – was in the kettle, and his latest book charts the rise, fall, mutation and rise again of this quintessentially millennial London sound against a backdrop of public policy decisions specifically designed to suppress a genre, its makers, its radio stations and its fans.

After a period of pop dilution, it has finally started racking up airtime and awards on its own terms

By and large, until the #grime4corbyn phenomenon of 2016, where a handful of prominent MCs came out to support Labour, this niche, granular form of disorienting high-speed music was not blatantly “political”, as a Billy Bragg fan would understand it. But while the story of grime, its key players and its evolution would have made a gripping book in itself, the genre is inextricably intertwined with the story of the capital, and its social and cultural politics over the past 20-odd years. Hancox is a tremendous guide to both.

He can look back from the vantage point of 2018, where this most underdog of genres has, after a period of pop dilution, finally started racking up airtime and awards on its own terms: Skepta’s Mercury for Konnichiwa in 2016, a No 1 album for Stormzy’s Gang Signs & Prayer (2017), and an MBE for grime’s “godfather”, Wiley (born Richard Kylea Cowie), whose role as mentor, mogul and den mother could easily fill two books (his autobiography is out in paperback next month).

The journey to mainstream acceptance has been, not to put too fine a point on it, insane. It wasn’t just barriers such as Form 696, the Kafkaesque mechanism by which the Met made it impossible to stage live grime nights; Hancox dives deep into the riveting minutiae of how grime (realistic, dressed down) was frequently pitted against UK garage (aspirational, dressed up) and plots the arcs of individual players – such as Rinse FM’s Slimzee, who got an asbo and suffered a nervous breakdown when the pirate station was raided in 2004 (it is now legal).

Ironically, Britain actually had the new punk rock on its hands. But while not averse to giving the heritage treatment to 1977, its (often white and middle-class) cultural gatekeepers could not, or would not, recognise it as such. And the powers that be did everything to conspire against it. The notion of “inner city pressure” was certainly operational when junglist Goldie released Inner City Life in 1995, but successive governments presided over more than two decades of social cleansing, gentrification and the closure of youth centres and defunding of offending prevention programmes. It wasn’t long, Hancox argues persuasively, before the student demonstrations of November and December 2010 turned into the riots of 2011.

If all this sounds overly professorial, it isn’t: Hancox’s love for the music – for its socially unacceptable, alien sound, its hyper-local reference points, and its refusal to become Americanised rap – cuts through like a siren.

• Inner City Pressure: The Story of Grime by Dan Hancox is published by William Collins (£20). To order a copy for £17 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99