You will need Maths A Level to do Economics at uni. I have two friends going to LSE in September to do it, and they both needed it. In fact, they had to have Further Maths, so that is something you should definately look into doing as well as A Level maths.
There is no point retaking GCSE buisness, while doing it at A Level. A Level is a higher standard, so if your school will allow you to do it, then retaking a lower level is a waste of time. Just concentrating on getting an A in A Levels (Cause you need AAA/AAB to get into good unis to go Economics).
Remember, Economics is a small part of a large field. There are lots of other similar courses, which may have less maths content.
Some examples:
- UCL - Statistics, Economics and Finance
- Queen Mary - Economics, Finance and Management
- Royal Holloway - Economics and Management
- University of Southampton - Economics and Finance
- University of Surrey - Business Economics
- University of Sussex - Economics and Management Studies
I've stuck to top 20-ish southern universities, as that seems to be what you are after. But you get the idea. Don't get too stuck into just Economics, look at all the options. Pure Economics is one of the most competitive courses out there, whereas the combo courses are less so, and still lead to the same kinds of jobs (Investment Banking, etc)