Mike Leigh isn't directing it, as far as we know, but there's still a definite sense of reunion about the news that Jim Broadbent and Brenda Blethyn will be lending their voices to **Ethel and Ernest{
Briggs' book, which won the Illustrated Book of the Year gong at the 1999 British Book Awards, is a tribute to his parents, and follows their lives from their courtship in the 1920s (when respectable Ethel was a lady's maid and socialist Ernest was a milkman), through the Depression and the Second World War, to the advent of newfangled technologies like television, and their deaths in the early 1970s.
Briggs is famous for children's classics like Fungus the Bogeymand and the Father Christmas stories (all adapted for TV), but is still probably best-known for The Snowman, the Christmas perennial that foisted Aled Jones on the world.*
Parallel to that career, however, is the one where he produces books for adults, like the Falklands War allegory The Tin-Pot Foreign General and the Old Iron Woman, and the devastating domestic nuclear war drama When the Wind Blows: the only previous full-length cinematic feature adapted from his work, in 1986 (spoiler: it's heartbreaking). Its protagonists, Jim and Hilda Bloggs (also seen in Gentleman Jim) are Ethel and Ernest in all but name, and the film's look (based, sensibly enough, on Briggs' illustrations) is probably a reasonable indicator of what we might expect here.
John Coates, who produced The Snowman, is also behind Ethel and Ernest. He's been putting the project together for at least a year (a full-length "animatic" already exists) and is currently shopping it at the Toronto International Film Festival.
*And it wasn't even him singing in the film!