[abb]

http://www.raf.mod.uk/history/rafhistorytimeline1939.cfm

6 Sep 1939 - South Africa declares war on Germany. Also on this day is the Battle of Barking Creek, when a error in identification in the Chain Home Radar system led to RAF aircraft engaging each other over the Thames Estuary. Blenheims, Hurricanes and Spitfires, not physically unlike the German Ju 88 and Bf 109, reported seeing enemy aircraft and several claims were made.

[GeronL]

6 Sep 1939 - South Africa declares war on Germany. Also on this day is the Battle of Barking Creek, when a error in identification in the Chain Home Radar system led to RAF aircraft engaging each other over the Thames Estuary

After that blundering bombing raid this must have been really worrying for the top brass.