I missed this announcement from Terry Pratchett on March 1, 2011 (with no way to do a direct link yet):

There has been one hell of a lot of rumours regarding a Good Omens adaptation over the past few weeks, mostly started by me at the SFX Weekender.  So, ladies and gentleman, I can hereby exclusively reveal that – YES – Neil and myself have shaken hands and received groats from Rod Brown sealing a TV deal. An official announcement from Prime Focus will follow in a couple of weeks time.  However, I can reveal right now that Terry Jones (yes, the Python) and Gavin Scott (not a Python, but he gets it) are already on the job.  It’s been a long time coming, but it’s looking good.