The daily 1938 flights Berlin to London were joint Sabena/Lufthansa, different carriers operated on different days.
Sabena had both Ju52s and SM.73s and 83s in use then on the London route. The Junkers were German, the Savoia-Marchettis were licence built by Sabca in Belgium. That is how things were often done in those days.
The times I have for August 1938 are only a few minutes off those quoted by Renfrew :
Berlin Tempelhof - 1435
Dusseldorf 1655/1720
Brussels - 1815/1830
Croydon - 2000
The aircraft overnighted at Croydon (hangared of course !) and returned to Berlin the following morning.
Sources :
Cooke Continental Timetable August-September 1938 (had air times)
The World's Airways (1938), chapter on "Belgian Airways"
Complete Sabena prewar fleet listing here
http://www.europeanairlines.no/Fleet_SABENA_170504.htm