Here are two short extracts from Tosca, broadcast by the BBC in 1938 and 1939. Both feature the famous tenor Beniamino Gigli and were conducted by Vittorio Gui. Each extract is under 4 minutes long, to fit on a 78rpm record and were recorded off-air by an enthusiast. This is all from either performance that seems to exist.
June 2, 1938 (3'55) 'E lucevan le stelle' with Eva Pacetti as Tosca
May 15, 1939 (2'39) ‘Recondita armonia’ with Aristide Baracchi as the Sacristan