At least on my older mag safe charger, only 2 pins are connected. You can pull off the UK plug and plug in the US or EU one, or even just a regular figure 8 lead (not sure of the correct name for these!)

Had a few times where I've had to disconnect the charger as I could feel an effect like static electricity on the metal case of the MacBook.

Oh wow! Sure enough, the UK adapter _has_ the ground pin, but it's not connected to anything .

https://apple.stackexchange.com/questions/17575/how-to-prope...

Alright if I sell any of this North American grounded version, I'll make one for y'all across the pond!

That's right, but the short version isn't connected to the ground. https://discussions.apple.com/thread/8594979

I just found this too. So strange to have a useless prong--maybe it's just for mechanical support? IMO if thats the case they should make the whole prong plastic to indicate its lack of electrical function.