That is a pathetic excuse; for Britain to squander all of those lives, and eventually lose its colonies, due to a war started to “protect Poland”, they ended up with a postwar world with Poland (and most of Eastern Europe) enslaved. Churchill knew they’d won nothing and lost everything; France turned out to be the smarter by sitting it out for the most part.
Churchill also knew Britain was going to lose the empire soon even if they didn’t enter the war.
You should also realize that the Poles and the Russians were still poking at each other over the exact layout of the border and at any time the Poles could go to war against the Russians or vice versa. Britain (correctly, IMHO) didn’t want to get involved in that, especially when it might be a war that Poland had provoked.
France sat it out because they had to. Go look at the status and doctrine of their army in the pre-war period. They were pretty screwed up for a number of reasons to the point where most of their tactics were oriented towards defense with very little offensive capability. If you want to see how screwed up they were (and you hadn’t looked in on recent scholarship on the subject), The Chieftain on YouTube has an excellent video on just how screwed the French tank corps was, despite having the best tanks in the world at the time. It’s a microcosm of how their entire army was.
https://www.youtube.com/watch?v=ZqoPZK6gyao
The only part of the French military that was really even vaguely offensively focused was their navy (with the all-forward-guns battleships and battlecruisers), and even it wasn’t all that clueful.