The BBC hardly ever commission programmes directly any more (so says my actor husband) and use production companies. Best advice then would be to find which production companies are most likely to be interested in your idea (check out what they're currently offering) and then find out the important people in those companies. My guess is that you'd find out a lot from the web and their websites, or careful reading of tv magazines like Radio Times, or investigate some of the industry publications.

As to how to copyright your idea - can't help there, I'm afraid, although you could do the old "send yourself a sealed letter by recorded delivery" wheeze, whereby you write your idea down and post it to yourself. The date on the package will prove that you had the idea at that point, if it ever came to the crunch. But I suspect there's not a lot of money in the idea alone, as what makes shows successful is a blend of design, presentation, camera work and other promotional stuff.