If you are still interested in pre-Hiroshima references to atomic bombs, Alan, the novels I know of are listed in a previous post. In the Times digital archive I found just two references prior to the Lords debate. One was from a September 1939 letter to the editor and was in relation to Hitler’s threat of an unspecified secret weapon; another was from the early 1930s and was the name of a racehorse which was scratched!

HRS Phillpott: Globe-Busting Bomb – It Was Coming.

““If what we are told about the atom is true”, he said, “every atom in the world might be disintegrated and the world would disappear.”

(This would be Esme Ivo Bligh, ninth earl, and the son incidentally of Ivo Francis Walter Bligh, former president of the MCC and Kent County Cricket Club and the first English captain of an Ashes match with Australia.)

Based on the phrasing used in the above quotes, it seems to me more likely that they are drawing more on some knowledge of the German bomb project, than pre-war discussions: atomic bombs are referred to quite casually, as though the listener ought to be aware of them (and while there were a few — not many — atomic bombs in pre-war SF, how many peers of the realm would have read about them, or remembered what they were in 1945?); and the statement is also made that they were something which were very nearly developed in the war, which is not something you could just assume from pre-war discussions. Given the context of the discussions about how to control German science and prevent revenge missile attacks, it all very strongly implies that some stories about a German bomb were floating about. But still, without seeing those stories I can’t be sure.