Origins

A map is useless without its key, to unlock its secrets, and this comes in the form of a book, the Map of Mysteries by Carol Gray.
   Carol (69) has been living with the Undergrowby gnomes for 33years now, ever since she lived in an old schoolhouse in the middle of nowhere. Along with the schoolhouse came a hedge-encircled overgrown school playing-field which, it turned out, was the home of the last remaining tribe of an endangered species of gnome.
   Once, long ago, these gnomes were woodland creatures who walked side-by-side with humans. Now, thanks to human misbehaviour, (fences, concrete, cars, grazing farm animals, etc.) they have been forced to evolve into a race of tunneling gnomads. Many years before Carol and her family moved into the ramshackle school house, they had popped up behind the hedge in that school playing field with its 4ft tall weeds and they had known this was somewhere where they would be safe for ever. 
   Then the schoolhouse was sold and along with its overgrown field and its hidden treasure, the hidden gnome village. Carol, her husband and family had planned to grow their own food in the field, but it never happened because, luckily for the gnomes, they were sentimental fools. 
     Touched by the gnomes' plight, they found themselves planting a new little woodland for the Growbies instead of a vegetable patch. They planted wild plants, fruiting shrubs, trees, a pond and a bonfire area. as well as the gnomes, an assortment of wild creatures moved in and made their homes there undisturbed.
  (Interestingly, many years later during her passionate studies into oriental medicine, Carol discovered that the spatial placement of all these features corresponded approximately with the perfect placement of the five elements, the eight winds, and the nine directions observed by the ancient Chinese scholars who speak through the I Ching, the Book of Change. The I Ching is said to be the first book ever discovered, its origins lost somewhere in the mists of time, (much like Undergrowby's and no doubt much like many other timeless, reliable old belief systems).) 
   Feeling a bit guilty for depriving the family of their dreams of a vegetable patch, and by way of helping with the mortgage, the Growbies taught the family how to make a range of very odd traditional magical artifacts out of clay, so they could make a living. That was the birth of Undergrowby Pottery in 1984. Carol is still making Undergrowby Pottery to this day, even though now she is getting very old. 
   A few years ago it was clear that the playing field would soon be too small to accommodate the growing population of Growbies, so the elders and specialist map experts, with their priceless lesser-known close-up maps, called a meeting in the meeting house. 
   The Map of Mysteries was consulted on what could be done about it. The message from the ancestors (whose spirits live in the map) advised a move towards the west, to a faraway land where the sun sets over the water and a tall metal tower points to the sky. "That's Blackpool!" said Carol Gray. She had been born there. No coincidence of course. 
  And so, trusting the map as much as the Growbies do, without a second thought, the schoolhouse was sold. Two removal trucks were needed, one for the humans and one for the Growbies, and a new Blackpool home was found. It was just far enough off the beaten track for safety, with enough room for a pottery and enough cellar space for the Growbies to build an underground village. It was perfect. Now, that village-in-the-cellar has tunnels connecting it with the whole of underground Blackpool and it is still expanding. It emerges above ground here and there, where there is plenty of cover.
The sandy Blackpool earth was perfect for digging tunnels and connecting the cellar with important useful locations like the beach, Jubilee Gardenson the prom, Gynn Gardens(a little park), the chip shop, weedy gardens in the neighbourhood, etc..Once they got going, popping up wherever they could smell a nettle plant, they realised it was going to be like doing a jigsaw puzzle. They would have to build this new Undergrowby in small sections,... an assortment of weed patches all joined by underground tunnels. 
The Lake District (when the tunnelers get there) will be proclaimed the new Watery Wetlands, but for now that honour is bestowed upon Fleetwood boating lake. South Shore, St Annes and Lytham is currently the Summerlands and the Pennines (when they get there) will be the new Rocky Headlands, but for now the Growbies are saying it is in and around the Rock Gardens on Devonshire Road. They are so determined to survive and to restore their land to its former glory, they will keep forging onwards, making something out of nothing, somewhere out of nowhere and calling it whatever they need to call it to recreate the map.
Bit by bit, Undergrowby will spread like seeds from a mother plant to cover the entire land again and wherever it seeds itself, everything will immediately be arranged in the right place according to the map. There may be hundreds of Undergrowby settlements before the year is up. But as long as there is at least one Land of Undergrowby somewhere, as long as it is loosely conforming to the map, their comical child-like civilisation will go on. When Carol Gray dies, someone else will no doubt be roped-in to help them.

That someone could be you. If you live in or near Blackpool, there may be a gnometunneling beneath your house right now, and if you have a nice nettle patch outside or, joy of joys, a wild hedgerow, they will be seeing you soon.