Naman Ramachandran As the days grow shorter and families hunker down cozily in front of the TV, British holiday programming has grown into a dependable export around the world, thanks to the success of Christmas specials for shows like “The Office” and “Gavin & Stacey.” “Demand for British content is higher than ever across the board,” says Louise McNab, director of content sales at BBC Studios, the commercial arm of the U.K. public broadcaster.