Eliza,
Just checked on google maps (search bar: "The Plough Roundabout, Hemel Hempstead" UK ) and that Magic Roundabout (marked as such on the map) is a real piece of art! It first appears as a large circle with six exits, but is really six small roundabouts connected in a large circle. And traffic in the large circle is both directions!
To go straight across you need to go left and through four roundabouts (painted in the middle of each intersection). Or similarly go right and through four... And traffic already in each roundabout has the right-of-way.
It is worse than that. As you approach the whole mess, there are two lanes, each with a painted arrow, left and right. If you want to go right, and turn where the arrow points, you are put squarely head-on to on-coming traffic! Instead, you must bear left swing around sharply to the right to get going counter-clockwise around the large circle.
And no one has "sorted anything out" yet (as of June 2012, date of the latest google map street view).

Bob

It's worth the entertainment value to check it out. google maps is your friend (in this case, anyway). "The Plough Roundabout, Hemel Hempstead ..."

Oh, by the way, for Worst Invention, I submit/vote for the bicycle seat. Granted it's better than no seat at all on the stem post, but still there has GOT to be a better design somewhere.