God’s Own Country, Francis Lee’s drama about a gay relationship between a Yorkshire farmer and a Romanian migrant worker, triumphed at the British independent film awards, picking up best independent film as well as prizes in three other categories.

The film, based on its director’s own upbringing, beat competition from The Death of Stalin and Three Billboards Outside Ebbing, Missouri, to take home the award for best British independent film, along with a best actor award for star Josh O’Connor, while Lee was awarded best debut screenplay for his script. The trio of awards were added to the previously announced best sound award.

Dark period drama Lady Macbeth was the evening’s other big winner, picking up three awards to add to the already announced best cinematography and best costume design. Florence Pugh was awarded best actress for her role as a 19th-century woman who takes desperate measures to escape a loveless marriage, while the film’s screenwriter Alice Birch took home best screenplay and Naomi Ackie received most promising newcomer.

Meanwhile, the Guardian’s Charlie Lyne was victorious in the best British short film category with Fish Story, a self-described “fishy tale” narrated by fellow film writer Caspar Salmon. Fish Story was directed by Lyne as one of the series of Guardian Documentaries currently viewable on the Guardian’s website.

Elsewhere, Rungano Nyoni became the first person since Anton Corbijn in 2007 to win both best director and best debut director for her magic-surrealist drama I Am Not a Witch, whose producer Emily Morgan also received best breakthrough producer. Patricia Clarkson won best supporting actor for her appearance in Sally Potter’s dark drawing-room comedy The Party, while Simon Russell Beale received best supporting actor for his turn as Machiavellian Soviet underling Lavrentiy Beria in Armando Iannucci’s satire The Death of Stalin, which had previously won technical awards for best production design, best make up and hair design and best casting.

In the best international independent film category, Get Out triumphed over The Florida Project and The Square, with the film’s stars Daniel Kaluuya and Allison Williams in attendance to pick up the award. Williams said she hoped the success of the film would see more “people take chances on film-makers with an unusual and daring vision”.

Kristin Scott Thomas presented Gary Oldman with the Variety award, which recognised the global impact made by the actor in representing the British film industry, while the special jury prize was awarded to Femi Oguns of the Identity School of Acting and Identity Agency Group, for his work in tackling the absence of BAME talent on screen. Veteran actor Vanessa Redgrave received the Richard Harris award, which recognises outstanding contribution to British film by an actor. Redgrave, who was presented the award by her daughter Joely Richardson and Harris’s son Jared, paid tribute to late actor Harris for having a “generosity and a spirit that are rare at all times”.

British independent film awards – the winners

Best British independent film God’s Own Country

Best international independent film Get Out

Best director Rungano Nyoni, I Am Not a Witch

Best actor Josh O’Connor, God’s Own Country

Best actress Florence Pugh, Lady Macbeth

Best screenplay Alice Birch, Lady Macbeth

Best supporting actress Patricia Clarkson, The Party

Best supporting actor Simon Russell Beale, The Death of Stalin

Debut screenplay Francis Lee, God’s Own Country

Douglas Hickok award for best debut director Rungano Nyoni, I Am Not a Witch

Best documentary Almost Heaven, directed by Carol Salter

Breakthrough producer Emily Morgan, I Am Not a Witch

Best British short film Fish Story

Most promising newcomer Naomi Ackie, Lady Macbeth

The discovery award In Another Life

Best cinematography Ari Wegner, Lady Macbeth

Best casting Sarah Crowe, The Death of Stalin

Best costume design Holly Waddington, Lady Macbeth

Best editing Jon Gregory, Three Billboards Outside Ebbing, Missouri

Best effects Nick Allder, Ben White, The Ritual

Best music Carter Burwell, Three Billboards Outside Ebbing, Missouri

Best make up and hair design Nicole Stafford, The Death of Stalin

Best production design Cristina Casali, The Death of Stalin

Best sound Anna Bertmark, God’s Own Country

Variety award Gary Oldman

Richard Harris award Vanessa Redgrave

Special jury award Femi Oguns