On 22 March 1941, a Blenheim of 139 Sqn was shot down by British AA fire near Lowestoft. I guess Brian had already this but the Admiralty War Diaries (available online at if your have a fold3 account) include a message by C in C Bomber Command to Air Ministry about this that is interesting. See
https://www.fold3.com/image/302108797.
Brian, if you don't have a fold3 account, tell me here and I wil copy the text.