Apparently plans are there for series 2 and it may well be limited to just the two series or continuing with the 3 part format. I'm watching episode 3 right now.
I was just looking on IMDB and someone has gone on a rant about how utterly ridiculous it is that they're bringing Zombies back to life in it and not realising just how stupid his comments are. Kinda funny really.
Looks like the ratings managed to stay fairly consistent over the run, around half a million per episode, hopefully that's good enough to bring it back.