I watched a funny episode of King of the Hill, where Hank entered a lawnmower race. Good show. And of course they made fun of the the slow speed which lawnmowers supposedly can get up to.
But I looked it up, and I would say maybe they hadn't done their research, for these suckers get up to a good clip! I pity anybody who'd get in the way of one driving at full speed.
I would have bet that this originated in the US, but it seems it's a British invention.