There are different sorts of economics degrees: some very quantitative, others with more of a politic, history or management focus.
If you are trying for one of the more quantitative courses (the most sought after are Cambridge, LSE, UCL and Warwick) you will need A Level maths, most probably an A*. Universities hold back from demanding Further Maths at A2 because not all schools offer it, and they don't want to discourage pupils from those schools. The general rule is that if your school offers it, you should do the A2. Advice my son received was that he should do as much maths as he could at school as it would be easier to learn in a classroom setting, rather than playing catch up at University.
Another reason for only demanding the AS is that LSE will not offer against the Further Maths. They want three subjects to provide breadth. Not all schools allow students to carry four subjects through to A2, so again they would be disadvantaging some applicants. Warwick do something similar by giving a standard offer on the lines of A*AAa, eg a fourth subject at AS only.
It is worth noting that places at the four Universities mentioned above are extremely competitive. They will be turning down a number of pupils with 3 x A* predictions. LSE, for example had 2,747 applications in 2013 for 211 places. It is also possible then to take as many if not more maths courses, as economics courses, in the course of a degree. Indeed DS says he is doing more maths than his friends who is studying engineering.
Other Universities will not demand as much maths, but there is a trend for economics courses generally to become more mathematical, with RG Universities often expecting at least an A grade. Exeter, for example, raised its maths requirements last year, and this year seems to be making A A A offers. If you are not keen on maths it is worth looking at the course content closely. The wrong course could be a miserable experience.