I have just returned from a month-long trip in the UK, France, Spain and Morocco. I took 40 Euro cash and returned with 20E in notes and some coin. It would have been 30E but I left my CC at the hotel and had to pay a friend back for a purchase. In England and Wales, CC was accepted everywhere. Ditto in France and Spain, even very out of the way hotels for a glass of wine. In Morocco, the only place I would have needed cash were the markets, but as I wasn't interested in trinkets, that didn't bother me.
In Japan last year, I also used the CC everywhere. One market-like shop wouldn't take CC under the equivalent of $30, but even a lot of food stalls took CC. I still have some USD, which is needed for tips. My tip from one hotel in Canada: add $10 or whatever amount to your room bill, and they will give you the cash to tip porters and other hotel staff. Very handy! Personally, I no longer take cash with me overseas.