In terms of research skills and the ability to write then History, Politics, Sociology, Social Policy or Law.
But as important will be a) that you enjoy the subject (and therefore are more likely to get a good degree result) and b) that you get involved in student journalism and relevant vacation work whilst you are Uni, c) you are prepared to put in the hard graft in a low level job (typically in region radio or a local paper) for a few years once you graduate.