Britain wasn't ready for war in 1938. Their military was in sad shape.
Actually the time to stop Hitler was 1936, when he crossed into The Rhineland, he issued orders to turn around if the French started shooting at them. Of course, there wasn’t a single bullet fired at them.
Plus, the Czech army would probably have given Germany a much tougher fight than Poland's army. Czechoslovakia had better natural defenses with their mountains, and their army was stronger than Poland's. The latter still employed many divisions of useless cavalry.
In Manchester's bio of Churchill he has some fascinating stories of dissident German generals who were ready to depose Hitler if Britain at the time of the Czech crisis (basically Chamberlain) would finally stand up to Hitler and denounce his steady bloodless conquests.
Chamberlain refused to acquiesce to the growing numbers of Brits who finally saw through Hitler and were demanding Chamberlain stand up to Hitler and give a position in the gov. to Churchill. That wasn't going to happen as Chamberlain thoroughly despised Churchill. Almost to the end Chamberlain thought he could deal/reason with Hitler. Of course, Hitler played him like a violin.