On death for interfering with the Royal Swans (or downing them when they should have been upped, whatever): it might have been a crime in the Middle Ages, but all such wacky offences (being obliged to practice the crossbow, shoot Scotsmen in York etc.) were wiped off the statute books in massive culls around 1850. Any mention of them being current is an urban myth.

I think high treason and arson in a naval dockyard were the last capital offences, abolished only a few years ago. High treason (crimen laesae majestatis) included the usual things like murdering the monarch and rebellion, but also compassing or imagining the death, wounding, or imprisonment of the King, Queen, or Prince of Wales. Which puts a bit of a damper on innocent speculation if you take it too literally.