The British plug serves the same point as an inset because there’s a bit of non-conductive material on the plug itself that goes into the wall. If it’s not fully inserted then the only thing showing is the non-conductive material.
It also has the thickest metal on the plug as far as I know. It’s probably the only thing that the British have ever engineered better than the Germans.
At some point in the past that was the only way to make the business run immediately when the boss said it needed to run immediately, and it’s been that way ever since