IGCSE

I am guessing that the former is through Cambridge University so why not ask them there?

From what I can gather from Google, the first one (despite its "pure" content) is preparation for A-Level, whereas the second is at A-Level standard and beyond (NB. The word "pure" is significant in that respect since as far as I recall, it is only at A-Level where a distinction is drawn between pure and applied maths). In short, the first is lower level relative to the second.