Other varieties of swan (Bewick's, Whooper etc.) aren't included in this.
My theory as to why we don't eat swans is because they're too difficult to domesticate and the wild ones are too rare to kill.
During these, representatives of the two companies are allowed one day to catch swans and mark them with either one or two notches on their beaks.
The eating of swans is a royal perogative and up until relatively recently killing one of them was a treasonable offence.
The queen has an official Keeper of the Queens swans (constable or something).
" and produced a swan feast for his father and some friends (I was abroad at the time).
He prepared it using a recipe for goose, and all who joined in the repast declared it to be like very tender beef and delicious.
The Swan Upping ceremony which takes place every July takes a head-count of all the mute swans on the Thames and marks them for ownership either by the Crown or by the Vintners' and Dyers' Livery Companies, which were granted their rights of ownership by the Crown in the fifteenth century.
Technically, the Crown owns all unmarked mute swans in open water, and the Queen only exercises her ownership rights on some stretches of the Thames and its tributaries.
For a good recipe, get hold of the hampton court palace royal tudor kitchens cook book.
(I reccomend the roast lemon salad.) One of the reasons that swans are not eaten is probably to do with the fact that swans are soverign property and therefore may well fall under the guise of treason or another archaeic law still punishable by death.
Because they have been protected for so long, that eating them has gone out of favour.
Like deer, they were once hunted to near extinction.
In addition two City of London Companies Vintners and Dyers have rights but most of the swans visiting Britain have no claimants of ownership. My late husband saw the male swan in our local park kill one of its own young (by drowning it) when the youngster refused to leave the pond of its birth.