[SteveR]

I think I found it.

AIR50/169/104

(it's listed under 605 Squadron, P/O Muirhead)

Pages 5-7 (out of 20 pages in the file) are the Combat Report for 9 May 40 from 13 Group Intelligence. It covers the interception of a pair of Do-17s by Red 1 and Red 2 of 605 Squadron (Edge and Austin) and by Red 1 and Red 3 of 43 Squadron (Ottewill and Simpson). The narrative goes back and forth between the two squadrons and if that's not confusing enough, the first full paragraph that begins on the second page begins by mentioning that Red 3 of 605 Squadron had returned to base with engine trouble and took no part in the combat.

If you don't read it very carefully...

And it certainly doesn't help that it's stuck in with reports from P/O Muirhead.

Pretty sure this is the report you'll be wanting to look at.