Well, if you want to consign the Head of State's legal and political independence to the rubbish bin of history, reject the overwhelming desire of the majority of HM's subjects to keep the Monarchy, and leave the constitutional safeguards governing Parliament at the hands of the Leader of the House (BUFF!!! NOOOOO!!!) or the Lord Chancellor (for as long as the position remains, appointed as he is by the PM), hanging would probably do the trick.
If, on the other hand, you want to turn Britain into a bland republic, squander billions of pounds on changing laws, title deeds, diplomatic missions, documents, livery, courts, the constituion, warrants and (to be rid of them altogether) that old-fashioned "Kingdom" reference in our national name, all in order to save the public a mere 67p per head per year, maybe shooting is a better option?
I'd rather still be seeing sights like this:
.... and not swearing my allegiance to a political executive, personally.