"...place of execution/beheading of Charles II" - not an episode known to the historical record. Charles died in his own time. And his father Charles the First was executed in Whitehall, down the other end of London.

Tyburn (pronounced with a tie) is at Marble Arch,and a very popular place of execution for the generality - highwaymen, and Catholic priests and so forth. It's quite near Speakers' Corner - I wonder if that tradition might have been a carry over from the crowds of spectators that used to attend on executions there for hundreds of years, and no doubt got haranged by orators on the scaffold and off it.