President Trump’s desire to “make Hollywood great again” by wielding his preferred economic weapon — tariffs — has sent a shiver through Britain’s film industry.

British producers, camera workers, costume designers and other film crew woke up Monday to Mr. Trump’s message that he wanted to impose 100 percent tariffs on films made in “foreign lands.” This threat is particularly alarming in Britain, where Hollywood blockbusters are a critical part of the industry.

“It came completely out of the blue,” said Philippa Childs, the head of Bectu, the British union for workers in the creative arts. “It’s pretty frightening.”

Last year, nearly 90 percent of the 5.6 billion pounds, or $7.8 billion, spent on film and high-end TV production in Britain came from abroad, mostly the United States, such as the upcoming “Jurassic World Rebirth” and “The Fantastic Four: First Steps.” Britain’s biggest and most esteemed studios are home to streaming giants like Netflix, Disney+ and Amazon Prime. For decades, productions have been drawn to Britain by its generous tax breaks but also its experienced work force, which has been making Hollywood hits since “Star Wars” in the 1970s.

Mr. Trump has, so far, not followed through on this threat, and it’s not clear how he would carry it out. But the British industry is still recovering from disruptions caused by the coronavirus pandemic and then the 2023 actors’ and screenwriters’ strikes in the United States, and the concern is that uncertainty about tariffs could wipe out that progress.