You will encounter plenty of content that requires prior knowledge, and the exams can test anything learned in regular maths in theory (this equates to needing to use something from A-level maths as a stage in a calculation). A key example is calculus, which is taught in normal maths. Further maths deals with this assuming you already are pretty good at integration and differentiation, and so plows straight into difficult integrals or unusual methods.
I wouldn't recommend anyone take further maths without normal maths, no matter the exam board. And I'm not even sure the board would allow it.