Hallowe'en in the UK is not the big costume drama that is seen in the USA.
Fancy dress is for the most part focussed on the meaning of All Hallows Eve - the night before All Hallows Day when the spirits, supernatural and magical beings are able to cross into and visit the Human world. So, lots of spooky / scary costumes - Witches, cats, ghosts, werewolves, vampires, zombies, ghouls, mummies - you get the idea, but not big on anything like Hetalia / other Anime & Manga themes (unless it's something like a Ryuk, a shinigami - most people wouldn't get that reference if you knocked ontheir door for candy anyway).
I used to dress up as a witch to answer the door when my kids were younger. They're getting too old to go trick or treating now (it's mostly for primary school kids or those under 14yrs in my area), so they dress up and answer the door in costume for the little kids who are trick or treating.
We get a lot of kids coming to visit our streets. Most years we end up running out of sweets!