Oodles and oodles of anchors

My family gets BBC World News on the satellite over here. I've watched it as much as everyday for a week staight, and I have never seen the same news anchor twice on that channel. The BBC seems to have a never-ending supply of new anchors. Ditto with their weather people. Where do they all come from? And where do they all go to after they finish their one shift at the BBC World News desk?