Of many things that most Europeans (and many non-Europeans) don’t really quite ‘get’ about Britian, the sliced, squidgy white bread ranks pretty high. There is a general north-east and south-west division in Europe on this very important issue of bread. Germany, and east and north of it, belong to the brown, wholemeal, multi-grain (often rye) bread region, whereas France and the southern European countries belong to the white, wheat bread region. Naturally this is a very broad generalization, and there are white bread consumers in brown bread region, and vice versa. However, even in the region where white bread is more common, or preferred by the consumers, it can be quite difficult to find the British style sliced white bread. White bread comes in the shape of rolls, baguettes and so on, and sometimes as square toast bread, but not in the way that British supermarkets’ bread shelves are crammed with sliced white bread.
There is a wider selection of bread in British supermarkets compared to a few years ago, yet they still seem somewhat exotic, and such curious breads are often priced more expensively than the sliced white bread. Bakeries, and even supermarkets in continental Europe, offer a large variety of loaves and rolls at much more reasonable prices. Whether British consumers can have a wider range of breads at a reasonable price in the future remains to be seen.
PS: I somehow doubt that the phrase the greatest thing since sliced bread finds resonance among non-English speakers in Europe. For many Europeans, bread should be cut fresh at the baker or supermarket, or after the purchase at home, and not pre-sliced.