It is celebrated just as it is in America. On October 31 children and many grownups in Britain celebrate Halloween just before All-Saints' Day. In fact the custom of trick or treating started out in the UK!
Long ago, British children belived that every year they were entitled to one lawless night of pranks they could not be punished for, and this was called Mischief Night. In many parts of the country Halloween was the night they chose, because then the tricks could be blamed on mischievous spirits. It was probably from Scotland that trick or treating spread to the United States.
But many, many years before that, the last night of October was Samhain Eve in the British Isles. The word Samhain came from the Gaelic samhraidhreadh, meaning "summer's end". Samhain marked the end of summer and the beginning of winter for the Celts, who lived in Britain long ago. The next day was the beginning of the Celtic New Year. Samhain Eve was a gap in the natural order, when the dead returned to their old haunts, and all kinds of supernatural beings, often dangerously powerful, swarmed to plague the living. In the Middle Ages the Catholic church tried to Christianize this pagan festival and perhaps to protect its flock from evil by making Samhain Eve the Eve of All Saints, or All Hallows Eve, preceding All Saints Day on November 1. The word Halloween comes from All Hallows Eve. November 2 became All Souls Day, when prayers were offered for the dead.
After the protestant Reformation British churches no longer allowed prayers for souls in purgatory, so All Hallows Eve lost most of its associations with the spirits of the dead. But in Scotland and Wales witches and supernatural beings continued to be recalled by bands of youngsters dressed up in ghoulish costumes, carrying Halloween lanterns. These lanterns were mangel-wurzels (large beets) or pumpkins hollowed out with a ghostly face cut into them, illuminated by a candle placed inside. And just like in America, today children in Britain continue to knock on doors to demand candy or small coins. In the county of Somerset in southwest England this is traditionally called Punky Night.
Halloween was regarded as a sort of crack in time, so people also tried to get glimpses into the future. In the old days villagers would watch for the spirits of next year’s dead walking through the churchyard at midnight. Even today, fortune telling ceremonies are still carried on unwittingly or half-jokingly in Halloween party games like apple bobbing. In this game, apples are floated in water or hung by a string, and grabbed by the players just using their teeth. Once caught, the apple must be peeled in one unbroken strip and the peel thrown over the left shoulder. The peel, they say, will form the initial of the player’s true love!
In another game, two apple pits or nuts, representing a pair of lovers, are put on the fire side by side. In southern England if they “pop and fly” the love is true, but if they burn together, the couple will part. In northern England and Scotland exactly the reverse is predicted!
Also in Scotland, small objects are hidden in a bowl of champit tatties (mashed potatoes) to foretell what the coming year will bring. Everyone takes a spoonful, and their destiny is revealed by the charm in their portion. A thimble means that a woman will not marry, a coin means wealth and a wishbone means that their dearest wish will be granted.
For many years the celebration of Halloween in Britain included bonfires burned to ward off evil spirits. This custom caused a change in the Seventeeenth Century many parts of Britain transferred the celebration of Halloween to Guy Fawkes Day on November 5, which commemorates the discovery of a terrorist plot to blow up the Houses of Parliament in 1605. (This is Spector's favorite as it celebrates blowing up the Government)! But during the past twenty years or so Halloween has been re-introduced throughout Britain from the United States.
You may want to try a spooky Halloween Quiz from the BBC!