The UK-AIP is published by NATS, an Air Traffic Service Provider, not by the UK- Civil Aviation Authority. They are 2 entirely separate entities (though you wouldn't think so, looking at their logos)
I know it all steeped in history of how the unified Ministry of Civil Aviation gradually got split up into airports (BAA) CAA and eventually NATS, but I'd have thought the responsibility for the publication of the information in the AIP should rest with the Authority, not with a Service Provider. Still, NATS do supplements, AIS and NOTAM, so I suppose it all fits in together.
I guess it doesn't REALLY matter who does it, so long as it's done well; in my experience it's done very well indeed...
Cheers,
The Odd One