Creme de mure is a blackberry liquor that is traditional in this recipe. However, you can easily substitute creme de mure in a bramble for some fresh blackberries with a dash of gin, muddled together until you have a lumpy liquid puree.
I actually make this without creme de mure as standard as it is difficult to find where I am. Plus a lot of people might find that they buy it for this recipe and it goes unused the rest of the time. I also actually prefer the look of the mashed berries and the extra fruit taste.