Three Billboards Outside Ebbing, Missouri, won the most prizes at Britain's BAFTAs, including best film and best actress.
Most wore black in solidarity with victims of abuse, but not all.
"As Martin said, I have a little problem with compliance. But I want you to known that I stand in full solidarity with my sisters tonight in black," said Best Actress winner Frances McDormand, who donned a black and red lip-printed dress for the ceremony.
Set in the US, Three Billboards Outside Ebbing, a dark comedy about a mother seeking justice for her murdered daughter, was written and directed by British born Martin McDonagh. His best original screenplay award was one of five trophies won by the film,
Gary Oldman took the top male acting prize for his portrayal of Winston Churchill in Darkest Hour.
While Guillermo Del Toro was best director for The Shape of Water.
The Duchess of Cambridge wore a black ribbon belt in an apparent nod to the women's rights campaign.