I'm not familiar with "Cumberland Brandy", but since nobody else has posted a reply. . .
It sounds as though it must be a UK term. Analogous to "Welsh Rabbit", perhaps? There is a recipe for what claims to be Cumberland Brandy at:
formatting link
I can't vouch for its quality or authenticity, as I haven't tried it. It appears to be a poor man's whiskey (without distilling) -- sugar, raisins and wheat (!?!?), followed by a second run (adding more sugar and water), then mixing the first and second runs together. I expect it would have a fair kick to it, but not a whole lot of flavor. If that's what you're looking for, best of luck.
Doug