If Getty Images is to be believed, Clarke sustained the injuries on his head after accidentally falling over at Speakers' Corner in Hyde Park. I thought I'd seen him there one night.
However, the BBC reports that Clarke tripped over getting out of his car in the grounds of Parliament (Speaker's Court, perhaps?) and hit his forehead on a step. "It's sort of spreading. It wasn't a black eye it was a lump on my forehead, but with blood seeping down or something ... "
Likely story Ken, you old soak.