I did A level economics in one year! Sorry to come in so late! I got an offer- I can use the A I got in economics last year, and need two more this year from Maths, History, or Philosophy. I's definately doable if you just get yourself a good textbook. There's really not that much to it (sorry to anyone doing economics!). But it did help that I'd done the GCSE, and had a teacher to give me a few private lessons to make sure I had the basics sorted. But, like the others, I'd say maths is more important, and you could do that in one year too. Why don't you like that idea?
All the best anyway,