personal statement for economics with actuarial science at southampton

In principle it might not be a big issue, although you could of course tailor the maths focus of the PS to refer more to the kinds of maths used in actuarial science, which would make it more relevant for that course but if also applying to maths courses elsewhere, still suitably relevant I expect (unless the course in question has no such coverage of those topics but in that case you probably shouldn't apply to it anyway if that's your interest!