Now 70, Linton Kwesi Johnson, AKA LKJ, doesn’t age; he just gets more LKJish. His signature look – the neat, triangular goatee, jacket, tie and trilby – hasn’t changed. Nor has his poetry aged, whether on the page or stage, and best performed by the man himself, his deep Jamaican voice infused with gravitas. An innate musicality has always carried the rhyme and rhythm of his work.

In his new book, LKJ writes without false modesty that, looking back, he sometimes finds his feat of straddling poetry and music “astounding”. Born in Jamaica and since 1963 based in London, he is renowned for anthemic reggae poems such as Inglan Is a Bitch. But this is a collection of prose, not poetry – reflections drawn from lectures, newspapers and journals on subjects ranging from the New Cross fire (or New Craas Massakah, as his poem called it) to the limits of Bob Marley’s genius.

LKJ cut his literary chops in the 1970s punk era, alongside innovators such as John Cooper Clarke and a stable of artists who stood shoulder-to-shoulder against racism. The pieces in Time Come span 50 years, and with its intriguing title suggest both a beginning and an end.

The writing is often flinty and flecked with passion; taut and reasoned, but on the edge of fury. Arranged chronologically, the essays serve as an archive of social and racial flashpoints such as the “sus” stop-and-search laws that created a hostile environment in Britain.

The collection is especially perceptive about reggae. Back in 1976, LKJ wrote that “music totally encompasses the lives of the oppressed in Jamaica”, Bob Marley’s Talkin’ Blues (“Cold ground was my bed last night/ And rock was my pillow, too”) being among the finest examples. Like those of several of his contemporaries, Marley’s lyrics were often inspired by a semi-vagrant experience, informed by his early years growing up in the impoverished Kingston neighbourhood of Trench Town.

Many of LKJ’s pieces feel nostalgic for the golden years of the 70s, when the birth of reggae aligned with the rise of Rastafari, and with campaigns for social justice and antiracist activism. There’s a poignancy to the reproduction of images and original pages taken from journals such as Melody Maker and Race Today, neither of which now exist.

For me, reading Time Come induces a kind of jealousy for the vibrant immediacy, for the unity across class and race in the push for social change. In the 70s and 80s rebel music was on the frontline, and reggae’s dub poetry (a term LKJ coined) had a transformative power, as his “scatter matter shatter shock” description implied.

In his most revelatory essay, LKJ cites The Souls of Black Folk as a key source of inspiration. Published in 1903, this book by African American scholar WEB Du Bois revealed the beautiful internal lives of black people whose humanity had long been denied by the dominant white culture. Du Bois argued that the arts enabled them to demonstrate that they were just as learned as their white compatriots; arts were a tool towards what Du Bois’s biographer, David Levering Lewis, called “civil rights by copyright”.LKJ, though, never “sought validation from the arbiters of British poetic taste”.

When, in 2002, he was honoured with a Penguin Modern Classics publication of his work, some critics implied that it was unworthy; that reggae poetry didn’t belong in the literary canon. That LKJ confidently includes such carping in Time Come shows how, aided by an earlier generation of Caribbean mentors, he achieved success on his own terms “from a position of cultural autonomy”.

The book’s last quarter reads as a prolonged eulogy for those mentors – Andrew Salkey, John La Rose and others in the London-based Caribbean Artists Movement (CAM, 1966-72) whose members sought to discover their own aesthetic to “rehabilitate their Amerindian inheritance and reinstate their African roots”, as Caribbean scholar Anne Walmsley wrote. The group’s radical ideals underpinned LKJ’s poetry in “incorporating the [Caribbean] people’s language and music rhythms” to reassert the region’s own tradition.

LKJ recalls that, aged 11, he left Jamaica for England armed with proverbs, hymns, folk songs and the sounds of mento and ska. When giving voice to his experience, he drew on the deep well of his Caribbean education, constructing verse that became “a weapon in the black liberation struggle”, making each gig a call to arms.

He now laments that his popularity may have curtailed his productivity. Spending so long on tour affected his ability to write new compositions. But as these essays reveal, it’s too soon to call time on this great literary warrior for equal rights just yet.

Given the neglect of the “sufferahs” in our society and the shameful assault on refugees, the grace and power of LKJ’s writing are as necessary as ever. The poem that gives this collection its title is taken from his 1979 album Forces of Victory, and warns of a day of reckoning: “Fruit soon ripe fi tek wi bite/ strength soon come fi wi fling wi might/ it soon come/ look out look out look out! […] it too late now I did warn yu.”

Colin Grant’s most recent book is I’m Black So You Don’t Have to Be (Jonathan Cape)

• Time Come by Linton Kwesi Johnson is published by Picador (£20). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply