For over three decades, my grandfather would regularly slam shut the door of his modest Orrell Park semi, sniff the air, adjust his canvas shoulder sack, and set off for Chile. Exactly how many times he sailed back and forth between Liverpool, Valparaiso and Viña del Mar we don't know, but his life in the merchant marine meant he was away more often than at home. My father remembers returning from school one day in the early 1950s and asking my grandmother who the strange man in the front parlour was. "That's your father, son," she replied. Given my tenuous ancestral connection to the sea and Chile, I baulked at Patricio Guzmán's suggestion, in The Pearl Button, that his native land – a slither of a country still vast enough to encompass the Andes, the Atacama Desert, and nearly three thousand miles of Pacific coastline – had never fully exploited its seafaring potential. That is my solitary quibble about the film. An impatiently awaited addition to one of the most signficant and consistently mesmerising œuvres in contemporary cinema, it is a characteristically melancholic, exquisitely beautiful meditation on memory, the life-giving properties of water, and the death-dealing depredations of colonialism and dictatorship.

Conquistadors and colonialists, Guzmán says, habitually and petty-mindedly gazed only inland. As venal as they were myopic, the invaders ignored the sea and turned from the foreshore in search of landlocked riches - to the detriment of the tribal peoples' of Patagonia and ecological balance; at the cost, he suggests, not only of the mercantile and maritime potentialities arising from Chile's geography but of something essential to the Chilean self and soul. The Kaweskar ('water people'), who from time immemorial had swept the Pacific coastline in rudimentary canoes to eek out a sustainable living from the sea, bore the brunt of European brutality and systematic ethnic cleansing. A peaceable nomadic tribe at one with the natural world, they suffered untold humilitations, soon fell prey to imported alcohol and diseases, were harried and hunted, and, eventually, all but exterminated.

Despite the horror of that historical moment, this section of the film also recalls the sense of wonder Claude Lévi-Strauss felt while conducting anthropological studies of Amazonian Indian tribes. He says of the Bororo: "They thought that through the village, through its organisation, they preserved the very image of ancient time, that their society was what its makers wanted it to be. The ceremonial dancers each embodied a mythological character, and as they embody, they are the character, who lives again, who is present. So, it was a society that had abolished time. And, after all, what greater nostalgia could we imagine than to abolish time, and then to live in a sort of present tense which is a constantly revived past."

Guzmán, no stranger to radical nostalgia himself, ensures that the water people do not go down to silence. He resurrects them with the help of Paz Errázuriz's stunning black & white ethnographic photography, sound recordings of a distant descendant of a once thriving people talking in the dying tribal tongue, and the tragic tale of  'Jeremy Button' - an Indian boy bought for a button and shipped to England as part of a cruel, inevitably disastrous Victorian 'civilising' experiment.

Guzmán rose to international renown with his seminal documentary triology The Battle of Chile(1975-1979). Ever since then, he has stubbornly and tenaciously, in film after film, held those who destroyed Allende's ardent dream of democratic socialism to account while insisting on the importance of memory. Less interested in trading routes and import-export charts than in poetic symbolisms of sky and sea, his increasingly lyrical films have mapped the continuities and catastrophes of history in ever widening arcs. As his lifelong project of retrieval and restitution has fanned out from dedicated focus on the victims of Chilean fascism, his enquiry into the past has deepened and widened too. Guzmán no longer dedicates himself exclusively to the task of recalling his country's darkest hour; in recent years he has turned his acute attention to our relationship to infinity and the origins of life itself.

The Pearl Button begins with a single drop of eons-old water encased and preserved in quartz, pauses to gaze upon ancient ice-blue glaciers, and then expands into the cosmos. It combines salutary reminders of historic genocide and the patterns of barbarism connecting the colonial and Pinochet eras with exquisite scenes of elemental natural beauty and illuminating insights into the centrality of water to existence. Anger in the face of tyranny and awe before universal plenitude sit comfortably side-by-side in the maestro's recent films.

Guzmán handles his multi-layered, finely textured material with a lightness of touch and elegance of intelligence that makes for compelling, ultimately uplifting viewing. He is a warm, generous, gentle man and his charming personality flows through his films, but his easy-going, softly-spoken delivery and intimate, lilting commentary are deceptive, for, as I imply above, he is nothing if not ambitious. In Nostalgia for the Light(2010), he looked upwards, to consider the mysterious enormity of outer space; in The Pearl Button, he plumbs the unfathomable depths of Earth's oceans, repository of our deepest fears and source of sustenance. Guzmán's films cut across time and space. Indeed, it might be argued that he does so himself. In Porto of My Childhood (2001), Manoel de Olivera said: "To recall moments from a distant past is to travel out of time. Only each person's memory can do this. It is what I shall try to do." Guzmán, too, has poured his own past into his films. His search for meaning in memory has taken us from the world's driest desert (the Atacama) to the world's largest archipelago (the inlets and lagoons off South-West Chile); from the deserts and oceans of Earth out, ever outwards into the cosmos.

Primarily, though, Guzmán's work is earthed in the local. He consciously tests the patience of international audiences by returning, repeatedly, to the Allende years and the Pinochet dictatorship. In his last film, he sifted the sand of history to show relatives of los detenidos-desparecidos ('the detained-disappeared') searching for remains of loved ones in the Atacama; in his latest, celestial splendour sparkles still but he delves beneath the Pacific's surface for signs of those erased. In the ruthless and indiscriminate slaughter associated with Pinochet, the military junta dumped countless corpses into the sea from helicopters. The bodies were tied to railway tracks so they would sink without trace. Guzmán exhumes them for posterity and, in ways typical of his habit of gliding between pointillist detail and wider themes, he extracts one woman's heart-breaking story from the discovery, on the ocean bed, of a button clinging, limpet-like, to encrusted russet metal. This, as much as the pearl button for which 'Jemmy Button' was traded, gives the film its title.

In gruelling sequences toward the end of the film, we watch re-enactments of the process by which the bodies were prepared for their mass grave. Although Guzmán relishes beauty he doesn't shrink from the horror. He has gradually developed a form capable of containing the complexities of existence, of thinking aloud, by shaping his own distinctive variant of a vibrant, fashionable form - the essay film - and stamping his own identity on it. The essay film is a diverse, discursive, heretical, hybrid, often magical, magpie form - like cinema itself. Fond of travel, it roams, restlessly, across time, and space – the better to breathe and think It juggles 'documentary, avant-garde and art film impulses' while edging across a tightrope pulled taught between the personal and the political, narrative and non-fiction, actuality and autobiography, all the while resisting the pleasure principles of conventional narrative forms. It slips the moorings of categorization to sail the high seas of abstraction, doubt, contingency and subjectivity.

Guzmán's films reflect these complexes and, above all, the essay film's close relationship to the political past. They insist on cinema's capacity to historicise the present; generate a politics and poetics of memory that resists organised forgetting; remind us of events, ideas, ideals, people, and possibilities that the powerful would have us forget; and enable us to think through the radical past from the vantage point of the triumphalist neo-liberal present. They testify that cinema canrecord and reveal, interrogate and intervene on behalf of the politics of hope; and that despite Milan Kundera's (limited) litany of history's forgotten horrors: 'The assassination of Allende quickly covered over the memory of the Russian invasion of Bohemia, the bloody massacre in Bangladesh caused Allende to be forgotten, the din of war in the Sinai desert drowned out the groans of Bangladesh, the massacres in Cambodia caused the Sinai to be forgotten, and so on, and on and on, until everyone has completely forgotten everything.'

Actually, Kundera was no more resigned to the memory loss and fatalism implied in that passage than his friend Kurt Vonnegut. The three words most associated with Vonnegut, 'So it goes' (words repeated like an incantation in his anti-war novel Slaughterhouse Five) must be set alongside three from Studs Terkel: 'Hope dies last.' Kundera, Terkel and Vonnegut all resisted, and warned against the erasure of memory. If, as Kundera suggested, the struggle of the people against power is the struggle of memory against forgetting, then Guzmán's films know which side they're on. As Michel Foucault says: 'Memory is actually a very important factor in struggle (really, in fact, struggles develop in a kind of conscious moving forward of history): and if one controls people's memory, one controls their dynamism . . . one controls their experiences, their knowledge of previous struggles.'

For Chile, Obstinate Memory (1996), Guzmán returned to Chile to screen The Battle of Chile in his native land for the first time, to a generation for whom the Allende years are not so much a distant memory as a suppressed historical lacuna. In 1995, Pinochet told a nationwide television audience: "The only way to solve problems is olvido ('oblivion') . . . Forget it, do no talk more about the issue, then you will forget and I will forget." Guzmán has resisted what Stuart Hall called "the oblivion factory" more consistently and effectively than any other contemporary director. Hall noted that cultural memory is particularly vital to post-colonial societies (in which a litany of ongoing 'truth commissions' and 'judicial reviews' are attempting to correct the historic record), because "identities are names we give to the different ways we are positioned by, and position ourselves within, the narratives of the past."

Oscar Wilde, for his part, said: "To give an accurate description of what has never occurred . . . is the proper occupation of the historian.' It follows that no 'true' history can be written from the victor's perspective. In recalling the egalitarian promise of the Allende era, Patricio Guzmán revitalizes Ernst Bloch's concept of our capacity to 'dream forward' toward a better future. In resurrecting Pinochet's victims and their ideals and resisting the erasure of human hope, he reclaims the future from the blood-soaked past. In returning, time and again, to the pivotal events that unfolded in one slender, splendid country in the later stages of the most destructive century in human history, he speaks for all of history's slain. To paraphrase Benjamin, he deals not with the wood and ashes of history but, rather, the living memory of the flames. The Pearl Button is yet another personal and political triumph from one of modern cinema's great masters.

The following interview with director Patricio Guzmán was conducted by Jerry Whyte on 16th October 2015 at the 59th BFI London Film Festival.