Both location and hour of Galland's claim match with the RAF Circus 284, during which 403 Sqn claimed two Fw 190s shot down. Either he mistook a Spitfire for a Mustang, or a reco Mustang wandered in the area, but in any case there were no Allied loss during this operation.
There was one Allied loss probably at the time, a Typhoon of 56 Sqn. 56 Sqn ORB is uncomplete: Form 540 says 8 Typhoons went on a sweep to protect B-17 coming back from Bremen, one was lost to engine failure and Flg Off Cluderay bailed out over the sea, was unable to get into his dinghy and finally lost his grip on it and drowned. A Walrus was sent to retrieve it but turned back after losing its Spitfire escort and then his W/T. Form 541 only lists 4 Typhoons on a sweep between 1425 hrs and 1545 hrs on the Dutch coast. Cluderay and the other men in his formation are not listed, and so no serial is listed for the lost Typhoon.
http://www.rafcommands.com/forum/sho...on-(56-Sqn-RAF) has it as DN478, and points to Galland being the cause of the loss, but the location is very far from Galland's claim.