LONDON - Dark comedy One Battle After Another was the big winner at Britain's top movie awards on Sunday, picking up six BAFTAs, including best film and best director for Paul Thomas Anderson.

It beat home favourite, the tearjerker Hamnet, and vampire thriller Sinners, which has a record number of Oscar nominations, in the big two categories in the ceremony, where Prince William and Princess Kate were guests of honour.

"We have a line from Nina Simone that we stole in our film. She says 'I know what freedom is, it's no fear'," Anderson said.

"So let's keep making things without fear, it's a good idea."

Anderson also picked up the award for best adapted screenplay, while Sean Penn beat his co-star Benicio del Toro among others for best supporting actor.

The critical hit also won best cinematography and best editing, totaling six prizes.

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Sinners, which has 16 Oscar nods, won best original screenplay for writer and director Ryan Coogler, best supporting actress for Wunmi Mosaku, and best original score.

Surprise in the best actor category

The biggest surprise was Robert Aramayo beating Timothee Chalamet, Leonardo DiCaprio, Michael B. Jordan, Ethan Hawke and Jesse Plemons to win best actor for his acclaimed performance as Tourette syndrome campaigner John Davidson in I Swear.

He accepted the award - his second of the evening after picking up the rising star prize - in tears, saying "I absolutely can't believe it."

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Asked before the ceremony what it would mean to him to win, Aramayo told Reuters: "I haven't even engaged with that thought to be honest with you, I just feel really, really lucky to be on that list of names."

Favourite Jessie Buckley won best actress for playing Agnes, the wife of William Shakespeare, in Hamnet, based on the novel by Maggie O'Farrell and directed by previous Oscar winner Chloe Zhao.

The film also won outstanding British film, but it lost out on the two major awards, including best film, where its home advantage had made it a favourite.

The awards, hosted by Alan Cumming, were the first joint engagement for William and Kate since William's uncle Andrew Mountbatten-Windsor was arrested on Thursday.

William, president of the film academy, presented the BAFTA Fellowship to Donna Langley, studio head at NBCUniversal.