At an old workplace, we had a piece of equipment with a European plug that we regularly had to shoehorn into a UK socket. It was a case of shoving a screwdriver or a pencil into the earth hole on the socket to simulate that pin being inserted and unlock the others, then fumble the EU plug into the live and neutral holes. (All while the socket was powered down, of course.)

Not particularly safe, and the result of someone who found you could buy equipment cheaper from Germany!