Why were the British people expecting war in September 1938?

Answer 1

If they were expecting war, it was not immediately between Germany and themselves. Hitler at the time was making threats and incursions against Czechoslovakia, but although Czechoslovakia was 'created' by the Allies (including Britain) after WW 1, a defense treaty existed only between that country and France, not Britain.

Up to then, Hitler had only annexed territories that had been part of Germany anyway until 1918, and the Austrians had themselves asked the Allies for a Union with Germany as far back as 1919 but had been refused. Czechoslovakia also had been partly made up of territories taken away from Germany after 1918 - most prominently the Sudetenland. And is was generally agreed at the time that Hitler's further-reaching ambitions were all directed eastward, not against France or Britain.

So at the time the British people never felt themselves threatened. But many feared that finally Britain would be dragged into some military involvement by a country or ally crying out for its help. So apart from a few 'cynics' like Winston Churchill, the public in Britain generally stood firmly behind prime minister Chamberlain's policy of containing Hitler's further ambitions by the Munich treaty.