There are a few major retailers don't take it, too (including my local petrol/gas station) so beware, but they are in the minority.
You will occasionally see a supplement for using it (that's legal here) but that's more common online.
Personally, I use mine most of the time, but your do need a backup MC/Visa if you want to avoid cash. The Lake District is the most likely to be problematic as you're going to find a lot more smaller business who will find the higher processing fees too expensive. Best to check first.