Blue Steel aircraft would use the missile INS slaved into the aircraft system
Ah! That explains something that I'd wondered about. I remember reading that commercial airline INS units were fitted as a temporary lashup for Blackbuck and I'd wondered why it wasn't a standard fit. Using the data from the missile makes a lot of sense as you don't need quite so much accuracy for the run home (or wherever you are going after weapon release).
Astro certainly qualifies as a self-contained system, but has a rather obvious limitation for a 24/7 capability. A lunar distance shot using the sun in the right conditions would give you a daytime fix. Did they issue tables for doing that? It's a pig of a calculation in pre-PC computer days to do the calc from scratch and would be hopeless at flying speeds.