Oh, I'm sure it might have been marginally effective in some very specific circumstances.

But that was far from the norm. In the hope that you might actually go and educate yourself somewhat on the topic, here is the Times report on the last public execution ever carried out in England, that of Michael Barrett on 26 May 1868.

https://www.arthurlloyd.co.uk/Timeline/Execution.htm

It certainly sounds like it had the effect you claim it does, doesn't it?