is there any one opting for public international law for this sept intake?

I am joining Kings and wanted to know about the career prospects apart from joining one of the UN organisations (which mainly means that you can initially get only assignments to work on from its various departments)

I am interested in working for the UNEP or the UNDP in the future or may be even a govt think tank.... but i am not sure about how to get there. can any one help?