The descriptions for these qualifications are (on the OU's main site - open in new window) at:
Here is a brief explanation of the similarities and differences between them.
BSc (Honours) Mathematics (Q31) primarily covers pure and applied mathematics, and at Stage 3 you study both, or choose to focus on one or the other.
BSc (Honours) Mathematics and Statistics (Q36) primarily covers statistics, together with the underpinning mathematics, with a focus on either pure mathematics or applied mathematics.
BSc (Honours) Mathematics and its Learning (Q46) covers mathematics, together with aspects related to the teaching and learning of the subject. You can choose to focus either on mathematics or on both mathematics and statistics
To some extent, the same modules can be studied on more than one of these degrees. And Stage 1 is identical in all three. So, it is often possible to transfer from one to another part way through your studies. This commonality is shown in this pathway diagram (opens in new window).
If you prefer you can opt to register on one of the following widely-recognised qualifications.
Diploma of Higher Education in Mathematical Sciences (W43)
Certificate of Higher Education in Mathematical Sciences (T14)
You could then transfer to one of the degrees at a later stage, if you wish.