A collaborative writing duo has won the £10,000 Goldsmiths prize for the first time in the award’s history, for a book which took 10 years to complete.

Natasha Soobramanien and Luke Williams’s Diego Garcia, described by judge Ali Smith as an “extraordinary achievement”, was named the winner of the prize on Thursday evening. It was the first in-person ceremony in three years for the prize, which “celebrates fiction at its most novel”.

The book is about two writer friends, Damaris and Oliver, who move to Edinburgh from London, where Oliver’s brother died.

There, they meet the poet of the book’s title, who tells them he was named for his mother’s island in the Chagos archipelago, which she and her community were forced to leave by British soldiers in 1973.

The pair become obsessed by the episode and the Chagossian people, and want to write about the community’s experience in solidarity. The book interrogates the powers of literature alongside the crimes of the British government.

Soobramanien, who is British-Mauritian, and Williams, who is Scottish, both used to live in Edinburgh. Soobramanien now lives in Brussels and Williams in Cove, west Scotland. Diego Garcia was a long-term collaboration, which took 10 years to complete, co-written across countries.

Chair of judges, Tim Parnell, said the novel is “by turns, funny, moving, and angry” and “as compelling to read as it is intricately wrought”.

“Against the dogmatism of the single-voiced fiction that informed the British government’s expulsion of the Chagossian people from their homeland, they respond not only with rigorous critique, but also with an understanding of the relationship between voice and power which shapes the very form of Diego Garcia,” he added. “A marvellous book which extends the scope of the novel form.”

Joining Parnell and Smith on the judging panel were author Natasha Brown and the New Statesman’s executive editor for culture Tom Gatti.

Smith said that at the novel’s heart “is an experiment with form that asks what fiction is, what art is for, and how, against the odds, to make visible, questionable and communal the structures, personal and political, of contemporary society, philosophy, lived history”.

Reviewing the book in the Observer, Anthony Cummins said: “Intimate yet expansive, heartbroken but unbowed, and a book about writing that is anything but solipsistic, it’s a stirring novel that lights a way forward for politically conscious fiction.”

The other books on the shortlist for the prize, which was set up with the New Statesman in 2013, included two debuts: Booker prize-longlisted Maps of Our Spectacular Bodies by Maddie Mortimer, and Somebody Loves You by Mona Arshi.

Also on the shortlist were Helen Oyeyemi’s seventh novel Peaces, Seven Steeples by Sara Baume and There Are More Things by Yara Rodrigues Fowler, which was shortlisted for the Orwell prize for political fiction.

The 2021 prize was won by Isabel Waidner for Sterling Karat Gold..