Surprised nobody has mentioned Open University which just happens to be one of the largest in the world - http://www.open.ac.uk/courses/qualifications/q62
On the third year you can choose from the variety of subjects: applied maths like fluids, optimisation, etc., pure maths, statistics related, and physics related. Very fun, but challenging.
The course materials were excellent as were tutors, I think Mathematics has always been a priority for them.
OU offers a course in it which starts Oct of the next year. I have BE in computers.