They work under the cover of night, armed with seed bombs, chemical weapons and pitchforks. Their tactics are anarchistic, their attitude revolutionary. Their aim: to beautify.
An army of self-styled Guerrilla Gardeners is growing across the world, fighting to transform urban wastelands into horticultural havens. To document and encourage their victories, one of the movement's top generals has written a handbook.
"On Guerrilla Gardening", by Richard Reynolds, defines the activity as "the illicit cultivation of someone else's land".
"Our main enemies are neglect and scarcity of land," said Reynolds, a 30-year-old former advertising employee who wrote the book after his website guerrillagardening.org became a global focal point for would-be green-fingered activists.
"Land is a finite resource - and yet areas like this are not being used. That seems crazy to me," Reynolds told Reuters.
"And if the authorities want to get in the way of that logic, then we will fight them - but peacefully - through showing them what we can achieve with plants."
As he spoke, Reynolds and several London-based troops were enthusiastically digging over soil in a rough patch of grass outside a tower block in the south east of the capital.
Defying darkness - and risking arrest for criminal damage - they continued their "attack" on the otherwise grim, grey surroundings, forking in a hefty load of compost and planting lavender and Paris daisies for a splash of colour and scent.
"WE WILL FIGHT THEM... WITH PLANTS"
Thousands of "troops" worldwide have now signed up to Reynolds' website - each with their own troop number - where they post reports and pictures of their battles, or "troop digs".
For those inspired to follow suit, his book outlines tips and advice on everything from the most suitable clothing and what kind of lighting and communication equipment to use, to how to carry out a "seed bombing" raid.
"Scattering seeds is the easiest way to guerrilla gardening," he writes. "You do not even have to stop moving to do it - GG (Guerrilla Gardener) 830 Tony releases handfuls of Welsh poppy seeds while driving along the M60 motorway."
Reynolds says he was inspired to write the book after his first nocturnal gardening experience outside his own 1970s concrete tower block in London, when he discovered he was part of a largely secret but worldwide movement.
"I began because I moved to a tower block and had no garden, and yet all around me there were bits of land that nobody was looking after - so I have made it into my own garden. But it's that one everyone shares and can get involved in," he said.
