World's End by Mark Chadbourn
When Jack Curchill and Ruth Gallagher encounter a terrifying, misshapen giant beneath a London bridge they are plunged into a mystery which threatens the end of the world as we know it. All over the country, the ancient gods of Celtic myth are returning to the land from which they were banished millennia ago. Following in their footsteps are creatures of folklore: fabulous bests, wonders and dark terrors - there are dragons buzzing jet planes and shapeshifters on industrial estates, but their existence threatens the very fabric of the modern world. For the first time in many years, the lonely places of the once peaceful countryside have become a no-man's land. As technology starts to fail, Jack and Ruth are forced to embark on a desperate quest for four magickal items from the barely remembered days when the myths first walked the world - the last chance for humanity in the face of powers barely comprehended.