Try Torrentroot. It's a torrent search engine thingie that I was introduced to last night. It searches out titles over a bunch of different torrent sites. You'll have to judge by the comments if they're "safe" though, but I think that's about the best we're going to be able to do for now. You might luck out, though, since you're Dr Who-specific and someone might know of a site specific to just that where people are sharing their own Dr Who torrents - someone on a Dr Who group might know of one, kinda like the little casual game site that I use.