Changing from Chemistry to Social Science

Hello!

I am on track to finish in Chemistry at a decent (top 25 perhaps) but not amazing uni, with first class next year. I have an internship with an economic think tank, as well as a year studying abroad in Hong Kong, and my intention is to change career quite significantly.

So has anyone ever heard of, or have any experience of, a change like this? I am aware in Economics there are graduate diplomas avaliable (Birkbeck) that offer a decent chance of acceptance onto LSE, Oxbridge master programmes. But if I were more interested in say, International Relations, I really don't know where to start.

Predictably my academic background excludes me from many master programmes for IR and the Social Sciences in general, so I was hoping someone might have advice in how to approach this...

Thank you!!