War of Words: Battle Rap in the UK (UK 2016: Dir Tom Worth and Craig Tuohy)

Like many people over the age of, ahem, 40 - well ok 50 - my experience and understanding of the battle rap scene (a fast, furious and frequently very funny offshoot of the more mainstream rap genre) has been limited to Eminem, the 2002 'rap odyssey' 8 Mile, and the mainstreaming of Professor Green, whose put downs and character assassinations, an important part of this movement, have successfully transitioned into his successful music career.

Worth and Tuohy's documentary on the UK battle rap scene was five years in the making, but with its intensity and (pardon the borrowing of the word) flow feels like it could have been put together in 48 hours - that's not a criticism - and its hour and a bit running time passes in a flash.

Part of the reason that the battle rap scene has remained underground, if far from un-noticed - just witness the crowds at the events on screen - is that the average content of the rappers' battles is so eye poppingly obscene that it wouldn't stand a chance of being shown on any mainstream media - not that they need it, their lives being filmed and broadcast almost entirely via social media.

War of Words expertly captures the rawness of the verbal attacks and the non violent, peace keeping culture that underpins their outbursts - as one describes it, they're like boxers in the ring who forget their differences once offstage. The timescale of the documentary demonstrates the scene's transition from a freestyle approach to a more rehearsed rapping style, without sacrificing the shock of the rhymes but allowing a wider and more diverse group of people to participate.

Apart from the live footage, War of Words is brilliant in its portrayal of the almost Hogarthian rapper population, with great names like Lunar C (comedy gold), Stig of the Dump and Eurgh, all competing for centre stage in a relentless display of braggadocio. But the film also takes some time to concentrate on decidedly ordinary rappers Marlo and Shuffle T who - as the film's publicity states - look more like internet nerds than tough hip-hop guys, as they prepare for battle against Detroit legends MarvWon and Quest MCODY. Unlike the smooth and perhaps more fluent US exponents of the scene, the UK rappers use rhymes less cliched, funnier (and sarcastic) with a rough round the edges approach that makes the contrasting styles fascinating viewing.

I admit it, I'm old enough to have lived through punk rock, and watching Tom and Craig's footage - expertly dividing itself between the battles and the personalities behind the mouths - is pretty similar to punk gigs of 1977; profoundly DIY, alienating to outsiders, but to those involved providing a close knit community of people sharing something very difficult to understand and appreciate from an outsider perspective.

Go see it.