The UK awards, known as BAFTAs, are often seen as an indicator of who will win at Hollywood's Academy Awards, held two weeks later.
As he accepted his award, Loach thanked his cast and crew, and the people of Newcastle, where they shot the film, and the Academy for "endorsing the truth of that this film says, which is that hundreds of thousands of people in this country know, the vulnerable and the poorest people are treated by the this government with a callousness and brutality that is disgraceful". Celebrities who are expected to walk the red carpet include Emma Stone, Ryan Gosling, Nicole Kidman, Andrew Garfield, Eddie Redmayne, Tom Hiddleston, JK Rowling, Aaron Taylor-Johnson, Sophie Turner, Meryl Streep, Felicity Jones and many more.
The BAFTAs differ from their United States counterpart in having a separate category for best British film. "La La Land", which has been sweeping award season thus far, has the most nominations with 11.
Barry Jenkins, director of best-picture nominee Moonlight, said, "People ought to speak from their heart". Following behind the Damien Chazelle-directed flick is "Arrival" and "Nocturnal Animals", each with nine nominations.
Prince William, who is also president of Britain's film academy, was to present the academy's lifetime-achievement honor to veteran comedian Mel Brooks during Sunday's ceremony.
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The director of I, Daniel Blake took to the stage to collect the first gong of the night and immediately apologised for giving a "political" speech so early in the evening.
Emma Stone, victor of the Best Actress Award for "La La Land", and Damien Chazelle, victor of Best Director for "La La Land", pose in the winners room at the BAFTAs.
Loach saw off competition from American Honey, Denial, Fantastic Beasts and Where to Find Them, Notes on Blindness and Under the Shadow to take the BAFTA.
However, co-star Ryan Gosling lost the best actor nod to Casey Affleck, for his performance in family drama "Manchester by the Sea".