Andrew Haigh's 45 Years has been named best British film at the 69th Edinburgh International Film Festival.
Starring Sir Tom Courtenay and Charlotte Rampling, 45 Years received its UK premiere at the festival and has been selected for this year's Michael Powell Award.
English director Haigh said it was a "fantastic" feeling to win the accolade for his feature, which sees a middle-class couple question their relationship as they prepare to celebrate their wedding anniversary.
The film was nominated for the Golden Bear at this year's Berlin Film Festival and won awards for both Rampling and Sir Tom. It will be released in the UK on August 28.
Haigh, who was presented with the award by actress Jane Seymour, said: "This is a real honour and made even more special when you consider the list of British films that have won before.
"All you can hope for when you make a film is that it resonates with people, and that is why receiving an award such as this feels so fantastic."
The film was selected by a jury chaired by LA Times film critic Kenneth Turan with actors Karen Gillan and Ian Hart.
The panel said: "This is a measured yet provocative film, a masterclass in understated acting that was the unanimous choice of the jury."
The award for best performance in a British film was shared between Rampling and James Cosmo, for his role in The Pyramid Texts.
Rampling, who was unable to attend the presentation at Edinburgh's Filmhouse, said: "It is an extraordinary moment when you are singled out when the craft that you have been perfecting throughout your life is appreciated and rewarded.
"It is thrilling and humbling and I thank you so much for giving me the chance to feel so proud."
The ceremony took place ahead of Sunday's closing gala, when the 12-day festival will come to an end with the premiere of Iona directed by Scott Graham.