This 7-hectare patch of lush tropical jungle owes its existence to Willesden's unique microclimate.

These dangerous rooftop animals are not true snakes, but actually mammals - one theory is that they are weasels that became adapted to living in chimneys and other artificial tube-like structures, losing their legs over evolutionary time as a 'squirming' method of getting about proved more advantageous. In Victorian days, they were the bane of chimney sweeps - some of the bigger specimens could easily eat a sweep whole and still have room for a roof monkey. The creature was immortalised in Edgar Allan Poe's chilling tale, "Cough," Quoth The Chimn'y Snake.

Number of legs: Just four vestigial stumps.

Appearance: A sort of living draught excluder.

Habitat: Chimneys, ventilation ducts, church organs.

Diet: Soot, children.

Social grouping: Chimney snake society is basically like a pan of giant evil noodles.

Reproduction: When in heat, a female chimney snake suspends herself in her 'nest' chimney, takes soot into her lungs and puffs it out of the top of the chimney in a sexy pattern. Male chimney snakes, seeing these saucy smoke signals, race to her chimney. The first one to slither there will dislocate his jaw and engulf the whole chimney pot with his mouth, breathing in the female's smoke puffs which now come at an urgent, pulsing rate. These vigorous puffs of smoke cause the male chimney snake to hack up a sticky parcel of reproductive phlegm from his lungs, which double as gonads. The fertile mucus splatters on the inside walls of the chimney where the female chimney snake gathers it up at her leisure, using a bony appendage shaped like a teaspoon. Precisely what she does next with the gamete solution is unknown, and probably disgusting, but at any rate: six weeks later, a shower of hundreds of shoelace-sized newborn chimney snakes will pop out of her chimney at 180mph, then rain gently down on delicate parachutes made of placenta, falling into chimney pots all over London, ready to start the whole majestic cycle of chimney snake life again.

Relationship with man: Bad. Victorians always resented the fact that hundreds of young chimney sweeps and children playing hide-and-seek were taken by chimney snakes each year. They hunted the creatures down vociferously. Unfortunately, the only effective way of hunting a chimney snake known to Victorians involved lowering a small child down a chimney on a fishing line in an attempt to lure the serpent up to the rooftop, where it could be safely doused in acid. The hazards involved in this technique were many and, on average, five children were killed for every chimney snake dissolved.

Useful byproducts: The long, flexible spine of the chimney snake is much prized by Goths as a sort of scary belt.

Threats: Santa.