You don't have to dig too deeply to uncover the sinister roots of Santa Claus.

In the depths of winter, when darkness reigns and the shadows are at their most menacing, a bearded old man descends from the sky, pulled by impossible ruminants, and gains access to your home. That's a story that's got to have unsettling origins, and indeed it does.

Quite how the Turkish bishop St Nicholas morphed over the centuries into the jolly gift-giver who lives with elves and reindeer at the North Pole is an amazing tale that's covered exceedingly well by Jeremy Seal in his 2005 book Santa: A Life. But what preoccupies Paul Hawkins is the darkness that lies behind the modern veneer, and how the midwinter festivals of Europe have been sanitised by the global brand of Santa Claus.

In this country, we generally don't realise that it's perfectly normal throughout Europe for Santa to come accompanied by a demonic sidekick. In Dutch legend, he's joined on his rounds by the controversially blacked-up figure of Zwarte Piet (Black Peter), who bundles naughty children into a sack and carries them off to Hell. Germany has Belsnickel (or Knecht Ruprecht, or Hans Muff, depending on the region). In Switzerland, it's Schmutzli, and Austria has the feared Krampus.

The point Hawkins wants us to appreciate is that midwinter was a harsh, perilous time for our ancestors, and it gave rise to some fearsome superstitions. It was when the most terrifying of things that go bump in the night came out to play, and also when the pressure of encroaching cold and lack of food prompted people to let off steam. This was the month of Saturnalia, the Feast of Fools and the Lord of Misrule, of the Wild Hunt of Norse legend. People, especially young men, got rowdy. Christmas was never a festival for children.

Nor was Nicholas such a gentle, retiring bloke, despite the kindliness that made him famous. He wasn't above backing up his interpretation of the scripture with his fists, or returning from Heaven to wreak revenge on an abbot who had displeased him. Nicholas was not just a giver of gifts to good children. He would also punish those who were bad - with a birch rod, if you happened to be Dutch.

Underpinning much of Hawkins's saga is the theme of the Christian church coming to various accommodations with the pagan tradition. When faced with the choice of stamping out or assimilating, the clergy tended to pick the latter, and St Nicholas became a device through which paganism was tamed. He was a lightning rod for attracting pagan beliefs, whether those were actual demons, young men who ran amok dressed in animal skins, or goddesses (like Perchta from Tyrol) who posed too much competition for the Christian God and had to be put under Nicholas's "watchful eye". St Nicholas was even powerful enough to co-opt Odin, who, according to legend, dashed across the sky on an eight-legged horse, throwing sweets to children.

In more recent times, the transformation of traditional Christmas lore hasn't been driven by the Church so much as by the seemingly unstoppable momentum of Santa Claus himself. American influences, like the 1822 poem A Visit From St Nicholas (better known as The Night Before Christmas) and the commercial artists who helped establish the red and white costume, have modified the mythology still further. It took a while. One 19th-century German postcard of the Weinnachtsmann ("Christmas Man") portrays him tying a child to a tree so he would have both hands free to beat him. But even Finland's evil goat Joulupukki has been radically updated to fit in with the new benign tradition, and the Icelandic Yule Lads have lost their troll-like origins to become cuddly figures dressed in the obligatory red and white. In becoming a global festival, what Christmas has lost is fear.

And, strange as it might sound, there's something a little sad about that. A child-friendly Christmas may be a great thing, but Paul Hawkins's informative and enjoyable book will have you secretly longing for a Yuletide which is that bit darker, more primal and even a little scary.