Quite some time ago, I read this blog post about dreamcasting Good Omens, if a TV version of it should ever actually come to pass:
http://www.tor.com/blogs/2012/05/the-two-southern-nancys-casting-crowley-and-aziraphale-for-good-omens At the time I had two reactions: 1) amusement that every pick for Aziraphale had been on Doctor Who; and 2) a sudden need for a TV show in which Russell Tovey plays an angel.
I just finished rereading Good Omens, and this post came to mind. I agree that he's probably too young for Aziraphale, but...can't you picture him as an angel, anyway? An earthbound angel, sarcastic and tightly wound and touchingly, tremblingly brave; exasperated and in love with humanity in equal measure? Yes, okay, I know - a lot of that is just George from Being Human with wings, but that is partly my point: he'd be so good at it.
(I never did watch his last season of Being Human. I got enough of a sense from the internet, without reading any real spoilers, that it was not something I wanted to see, given that I had signed on to the show for "snarky supernatural flatmates" and not "an all-the-bad-things buffet.")