The British Admiralty War Diary for 12 August 1944 starts here in fold3:
https://www.fold3.com/image/1/301325052
A short extract:
"The watch on the North Biscay coast was maintained today by force 28 (Diadem, Onslow and Piorun) assisted by E.G. 3, E.G.11, E.G.12 and aircraft."
A quick scan of the more detailled pages for Biscay operations (around page 795) shows no mention of rescued airman, such event will probably not been recorded in a diary of this (worldwide) level.