From what I’ve gathered, the majority of feathers are legal to keep if they were obtained legally (eg roadkill or loose feathers that you didn’t disturb a nest for etc), but I cannot seem to find any info online about swan feathers specifically.
I feel like since it’s not legal to take a swan that didn’t die unlawfully (eg roadkill) because of them belonging to the crown or something along those lines then it probably isn’t legal to keep feathers, especially since you can’t tell from looking at a feather if it was plucked from an illegally killed swan or if it was found (kind of the logic behind all wild bird feathers usually being illegal to keep in the USA). Its just frustrating to not know for sure, and I’m sure a lot of people pick them up without realising.
I would like to know as I do enjoy finding pretty feathers when I go on walks, but obviously I don’t want a fine or prison time over a misunderstanding like that