The Student Room Group
So long as you could prove to any school you applied for a job at that you were qualified enough to teach politics (ie either your degree or A Levels included politics etc) then you can teach it also.

A PGCE gives you QTS status which them means you can teach whatever you want at any school (primary or secondary). The only thing stopping you from doing anything is a school not feeling you are qualified to teach something...ie there is no way I could ever convince a school that I'd be able to teach a language, so could never teach languages ( as all I have is a Spanish GCSE). But if I'd done, say Maths with Spanish at university and then did a Maths PGCE I might be able to convince some school somewhere to allow me to teach Spanish some of the time too.
Reply 2
Ok that's cool. My degree is politics so I should be fine! Yay!