Bohemia Moravia Protectorate
Airmail postcard from Praha to London during the period of German annexation of Bohemia Moravia that preceded the start of World War II.
The circular purple cachet 'D.K. / PRAHA 25' indicates it was inspected for Currency Control: Devisovou Kontrolou, applied at Praha.
How can anyone check a postcard for currency? This is regarded as a form of censorship and was in place for 6 months from April 1939.