Nathan Herbert sends proof that he owns and uses a three pin, inline plug and has lived to tell the tale, though it's questionable as to whether he can get through airport security with it! He writes:
"It's not quite the death trap artistic device as imagined by some people. Each of the plug-prong 'faces' is removable, and only one of the cube faces has live connection pins inside. The face opposite the live one has a standard UK socket on it. It's not bad (or lethal!) to use, just a pain to pack, as it's like packing a caltrop in your suitcase, and just as much fun to step on while jet-lagged in the night!"
Apologies to the artist who designed the HSBC advert!