Manchester is good for Economics. If you want to specialise in Economics do their BEconSci programme, Manchester has a lot of other courses which are basically interdisciplinary for people who aren't hardcore economists but want to get a more quantitative social science education. I reckon if you have an interest in politics/social policy/sociology you would get more out of doing Manchester's BA Econ programme than you would doing a straight politics/social policy/sociology course somewhere, because the economic knowledge will underpin what you learn in the others.
Manchester offers more of these interdisciplinary options than other places because it is pretty good across the board in these social sciences especially at research level. In the last RAE (which is IMO the most important table) Manchester was joint top for sociology, just below the top ones for economics and politics in which it came out with the same scores as Cambridge for both. That's not saying a Manchester degree is going to open quite as many doors as a Cambridge degree, its saying when the RAE assessors checked the quality of research done there, they were on a par.
The've also got a lot of strong research centres which overlap - Institute of Social Change, Brooks World Poverty Institute, IPEG, Manchester Centre for Political Theory, so they are good for postgrad and research students in the social sciences who have interdisciplinary interests.
Overall I'd say Manchester was a good place to be going if you are an economist with an interest in politics and social issues. Most of the people who come on here bashing Manchester are the ones focused on private sector banking and City jobs, maybe it isn't in the "in" crowd for the investment banks then, but it is rated very highly on the RAE.