Just a thought Cyflyer
Was he a member of Cambridge University Air Sqn ?
Using that as a search term - I got this result on Google
If he was a member of CUAS from 1938 - he could have already been a fairly experienced pilot by sept 1939.
Knowing how google search returns 'work' (in that they sometimes 'jumble' info) - the reference to Wop/AG on 75 NZ Sqn possibly does not refer to Chris,also the reference to Trinity and CUAS may or may not refer to Chris but it would perhaps fit in with his RAF career.Of course none of it is visible when you use the link to RAF Unit Histories so it must be information from a 'cached' page of unit histories.