A centuries-old insurance document detailing the trafficking of enslaved Africans began with the words: "In the name of God, Amen." For Dr Errol Francis, the artistic director and chief executive of the arts and heritage charity Culture&, the contradiction was striking: an invocation of God in a document that treated human beings as cargo.

It gave him an unusual idea: what if the documents that once insured the trafficking of enslaved Africans could instead be used to create a requiem in their memory?

The new work, Atlantic Requiem, by the Manchester-based composer David Önaç, will premiere on Sunday at LSO St Luke's in London, performed by the London Symphony Orchestra and BBC Singers.

Commissioned by Culture&, the project grew out of research into Lloyd's of London, the historic insurance market whose members helped insure ships and enslaved Africans during the transatlantic slave trade.

Sponsored by Lloyd's, the 40-minute, five-movement work brings together Catholic liturgy, historic insurance documents and testimony concerning the killing of an enslaved African woman aboard a ship in 1790.

Its musical language combines contemporary classical composition with jazz, gospel and other traditions that emerged on both sides of the Atlantic.

The performances, taking place during Black History Month, will be conducted by the Grammy award-winning conductor Malcolm J Merriweather. "This is a really complicated situation in how religion is being used. Religion was used to convert the indigenous people then, the indigenous people often took up religion as part of emancipation," Francis, who was a member of the steering group overseeing research into Lloyd's historical involvement in the transatlantic trafficking of enslaved Africans, said.

"That was why I thought to myself, 'Maybe we should write a Requiem Mass, because that would really bring out these contradictions and also use these documents for a different purpose than what they were intended for.'" When Culture& approached Önaç about Atlantic Requiem, he jumped at the opportunity. "The styles that I'm interested in come from both sides of the Atlantic, so it just felt like I finally had this grand canvas on which I could explore these dual interests, allow the two styles to enrich one another," he said.

For Önaç, who is of mixed heritage and hails from both sides of the Atlantic, the piece was an opportunity to explore longstanding questions about where he belongs.

"As a pianist, sometimes the piano itself and the layout or the geography is an inspiration to me," he said.

"When you took the five black notes and two of the significant white notes from the other set, you got this seven-note blues scale, which is the product of the musical and cultural experience of enslaved Africans from the other side of the Atlantic." But while the work ultimately moves towards reconciliation and joy, some of its most harrowing passages confront the violence of enslavement directly. The second movement draws on a 1791 grand jury testimony concerning the killing of an enslaved African woman aboard the brig Polly commanded by James DeWolf.

The testimony, preserved by the Newport Historical Society, records the account of John Cranston, a crew member who described a horrific incident during the ship's voyage from Africa to the West Indies in 1791.

According to Cranston, an enslaved woman suspected of having smallpox was bound to a chair, gagged and thrown overboard on the captain's orders, amid fears she would infect others aboard the ship. "There's bits in it that I get tearful even just talking about it," Francis said. "It is about people who've passed away, but it's also about the fact that we have survived this incredible trauma." For Önaç, the combination of the words and the music were at times so powerful that it felt overwhelming.

"The captain's words were that he was sorry because he'd lost such a good chair," he said. "I felt we needed to hear and see and experience what the human impact is here. What is the emotional impact? What is the loss of culture? What is the blindness to value?" Lloyd's has acknowledged its historical links to enslavement, and after the publication of the Underwriting Souls interactive archive, it announced its Inclusive Futures programme aimed at supporting Black and ethnically diverse communities.

For some, this artistic project doesn't go far enough. But Francis is careful to distinguish the requiem from important questions of financial redress. "It's not about reparations; it's about an artwork that acknowledges the suffering, but also the survival of African people," he said.

Önaç added that the requiem is not only a response to historical atrocities but a commentary on modern society. "Everything's so polarised and segregated and polemical right now, it seems to me, and I've tried to portray that in the black and white notes. "It's not just for then; it's a commentary on now as well."