For what its worth here is part of the passage from the book "Hatching an Air Force" by Peter Ilbery, which prompted me to ask the questions in the first place.
Am I wrong to assume this indicated clear weather, as he was "enjoying the outlook over the channel" and was able to see the FW's approaching at very low level?
Yeah, just skimming the book, the official report for Bournemouth says it was brilliant sunshine, one of the witnesses says beautiful clear day, another a bright sunny day, another beautiful warm sunny, etc.
The 1 Sqn pilot (Hastings) says fine, sunny, slight haze:
The official report for Bournemouth says 6-12 miles visibility.
Your initial post also asked about losses - will try to scan them in and post tomorrow, no guarantees though as various family things have to be taken care of.