They dont require you to have A-Level Maths (although this may depend on the admissions tutors). In the prospectus it says AS Maths is highly desirable. Part of the Philosophy course at Oxford includes Logic, and I'm pretty sure that that requires some mathematical proof (which you do in A-Level Maths), so even if you drop economics after your 1st year, they may give you more technical, mathematical logic problems.
they will read your personal statement, and Im sure you are likely to place more emphasis on the politics and philosophy side, especially if you're not applying for PPE elsewhere. For the entrance test, there is an economics section which is pretty much maths. You have to show some sort of knowledge and ability to manipulate and use formulae. That said, very good GCSE grades (although they might prefer A* in Maths), an excellent PS and school statement, along with a fairly good interview, could get you a place...
You want to avoid the econ, but you have to pass your econ prelim to even get the chance to drop it. You'll probably need to work harder at the econ, but if as you say, you are much better at the politics and phil, then you'll need to prioritise, if and when you get there.
i'd suggest going to the library, having a look at some 'Introductory maths for economics' etc. See whether you think the maths is accessible or not. You'll have forgotten a lot since GCSE, even if you did get an A, and you'll probably need some catching-up to do. Ive got Mathematics for Economics and Business by Ian Jacques - its the main maths text for econ for my college (hopefully mine anyway). Its not too scary...honest!