You can start Economics without any knowledge of anything like I did. Maths can be useful. In AS, we learnt about 5 VERY easy equations but the majority of it will be in A2 (still very little maths). It's easy to understand if you have a good teacher. You draw a lot of graphs
I had a B in maths and english GCSE (and most of my other grades) but I finished AS with A in Econ and AB for chemistry and biology so maths isn't that important but you will need good straight to the point writing skills whilst linking up theories.