I'll let the newly returned Geoff explain the arcane mysteries of swan upping.

Lord Nelson, the Admiral who destroyed Napoleon's navy, and then did it again, did have a run of bad personal luck in combat. First he lost an eye, then an arm, and eventually, at the Battle of Trafalgar where Napoleon's dreams of naval conquest where decisively and finally smacked down, he died of wounds suffered during the battle. Now, he stands on a very tall column in a very large square.

He also features prominently in the underground turntable hit "Upright Exemplars of British Manhood":

Horatio Nelson was a man.
A small British man with a master plan,
Of cunning and charm replete.
Horatio Nelson was a man.
The man to defeat Napoleon's fleet,
to sweep that fleet right off its feet.

- Count Dolby von Luckner

I only recently learned about the Swan Upping Ceremony when I was looking on the internet for something both British and silly that could somehow cause Lord Nelson to lose an arm.

There are lots of traditions involving royalty eating swans and claiming all unmarked mute swans for their dinners. Somehow, the Vintners and Dyers got in on it as well and now, every year, a swan census is taken.

Apparently there are non-ceremonial positions, like the Queen's Swan Marker, that are responsible for swan awareness and clearing the swans off of the Thames for regattas.

I hope the jaunty cap with the swan feather in it is part of his official uniform.

--Geoff