In Germany the acceptance for credit cards only became large scale after the interchange fee was limited. Today, most stores that accept card payments also accept credit cards, but only MasterCard and Visa. Using an AMEX as your primary card would be a pretty bad experience, because you'd constantly need a backup.

With that said, I'm happy most merchants don't put up with the humongous fees—in the end the prices are just raised to compensate for them.

Acceptance of Amex stands at just over a third of retailers UK wide. For London it is more like 50-60%.

Source: used to work as a CC payments analyst.

My experience in Glasgow, FWIW, is that the majority of independent shops/cafes/etc. don't take Amex.