Hi MuMu, this looks like a British recipe to me. I don’t know what butterfat level the British Sweet Cream usually has—but I agree with Patrincia that just about anything from milk to heavy cream should work. It just depends on your tastes.
I often speak with British and Australian folks in my “day job” (well actually I work evenings, but…) British English has some difference from American English and “biscuit” is one of those words that means different things on different sides of the ocean.
British “biscuit” = American “cookie.”
British “tea biscuit” is usually a rather plain cookie to be served with tea. They tend to be on the thin and dry side rather than the thick, soft or chewy side. They’re sort of like a sweet cracker—a paler version of Graham crackers.
Some supermarkets will carry them in the imports aisle, or sometimes they’re in the cookie aisle.
I bet this recipe would work well with graham crackers, or Nabisco’s vanilla wafers or chocolate wafers, as well.
Believe it or not, there’s a British site that rates various brands of tea biscuits!