‘Wherever the British settle, wherever they colonize,’ observed the painter Benjamin Robert Haydon, ‘they carry and will ever carry trial by jury, horse-racing and portrait-painting.’ This doesn’t sound like a bad set of cultural baggage, even for those who don’t care for the races. There is clearly a lot to be said for trial by jury, and portraits make up the most enjoyable — in fact, downright humorous — section of Artist & Empire, a curious new exhibition at Tate Britain.