@Will Armstrong your those GCSE's are probably below average, but they're certainly not going to prevent you from getting in, stuff such as the TSA is much more important.
Also, on the note of how Politics etc is regarded, obviously I don't have an inside knowledge of the process but they're not going to blacklist you for it, it's certainly not considered with the likes of Media Studies. Most people I met at interview did Politics at A level, it's only natural really that many potential PPE'ists are going to have Politics as an A level, they're not going to penalise you for taking an interest in one of the branches within your academic studies.
Fwiw, my AS levels were Business Studies, Economics, Politics, History. I think the Business Studies was a negative factor in my application (although this was marginalised as I dropped it for A2), but I don't think the Politics was a negative at all, if it was, I doubt I'd have got an offer, especially considering I got AAAB (B in History) at AS level.