“First, it is high treason to “compass or imagine the death of our Lord the King, of our Lady his Queen, or of their eldest son and heir.” The terms “compass or imagine” indicate the premeditation of a murder; it would not be high treason accidentally to kill the Sovereign or any other member of the Royal Family. However it has also been held to include rebelling against or trying to overthrow the monarch, as experience has shown that this normally involves the monarch’s death.”

Wikipedia is marvelously dry sometimes, this on the UK’s High Treason laws. And well done to Richard75 who added that rather good turn of phrase on the 21st March 2006.