Gazing across the River Douro at night in Portugal’s second city Porto is a bit like looking at the shelves of a rather well-stocked off-licence. Because what you see shining out of the darkness on the other side of the river are the illuminated names of some very familiar brands of port — Sandeman, Graham’s, Taylor’s, Dow’s, Cockburn’s — and others that mightn’t be quite so familiar, like Cálem, Cruz, Fonseca and Ramos Pinto.