It also has some distinctive theme music.
What I didn't realize until today is that the theme music is played on a theremin.
What is a theremin, I hear you scream? It was the world's first electronic musical instrument, invented by a Russian physicist in the 1920s. It consists of two aerials at right angles to each other. Put your hand close to one aerial and it raises the pitch. Putting your hand close to the other raises the volume. Moving your hands inside the two electromagnetic fields creates music.
So here is Celia Sheen, Britain's foremost classical thereminist, who is in fact the musician you hear in every Midsomer Murder. I know it looks like she's waving her hands in mid-air, but she really is playing the theremin.