She was present when King George VI and Queen Elizabeth visited the family estate at Hyde Park, New York in an effort to court American support before the second World War.

And that’s about it. It’s not the strongest premise for a movie, though Hyde Park on Hudson somehow contrives to make it seem rather less than the sum of its parts.

It’s a shame, too: we did want to like Bill Murray’s twinkling, canny FDR, but there’s not much the actor can do with a screenplay that’s lazily tacked together by a flat, wittering voiceover from Laura Linney’s Suckley.

The rest is a Rocky Horror Picture Show waiting to happen. Most of the girls will come to screenings dressed as Olivia Williams’s implausibly comely Eleanor Roosevelt. The audience will leap to their feet with delight when the car pulls over during a countryside jaunt and wobbles to indicate that FDR has made it to third base. The biggest cheer of the night will be reserved for the future Queen Mother (Olivia Colman) as she channels Dame Edith Evans’s Lady Bracknell: “A. Hot. Dog?”

There’s a surprising amount of hot dog-related banter and incident throughout this screamingly (and unintentionally) camp historical drama. For the visiting royals, “The. Hot. Dog.” is another bizarre manifestation of American culture to contend with: “It’s so confusing,” complains the queen, “We have a Hyde Park in London too.” Ho ho. Will those British snobs ever learn to love their coarse Yankee counterparts? You’ll have to wait until the hot dog-themed denouement to find out.

Pretty, buffering shots of the English countryside (standing in for upstate New York) do little to dispel the notion that Hitler might pop around at any moment to crash the party: “Carry On, Mr President.”