The Kensington Roof Gardens was originally created in 1936-38 as the apex of department store Derry & Toms and was later taken over by fashion house Biba, whose black and white wallpaper still decorates the staircases.
Now owned by Virgin tycoon Richard Branson and standing adjacent to the Babylon restaurant and nightclub, the garden is usually frequented by partygoers. But what many people don't know, and should take advantage of, is that it is possible to visit it with permission if no function is being held.
Garden designer and former ad executive David Lewis is the current head gardener, filling a role that encompasses caring for the gardens' new arrivals, the greater flamingos Splosh and Pecks - which have joined Chilean pair Bill and Ben - and overseeing the current renovations of the garden.
"Originally, the plan was just to make cosmetic changes," says Lewis. "But what we've actually ended up doing is a whole revamp."
The garden is split into three main areas: a naturalistic woodland garden, a Tudor garden and a Spanish garden. It was designed by Ralph Hancock, whose work Lewis says was considered "a bit out there and weird".
As the garden celebrated its 70th anniversary last year, it was felt the time had come to renovate it. While some of the original trees are still going strong, despite growing in only 40cm of soil and needing heavy pruning, some of the planting had become tired. So historical research was undertaken by consultants to learn how each of the garden sections appeared over the decades.
The woodland area is not reverting to a particular period but will be managed using 21st-century environmental practices with the help of consultant Fern Alder, says Lewis. Shrubs have already been cleared and the lawn will be extended, opening up views across the stream. More than 1,000 native British plants will be added, and composting and wildlife will be encouraged, particularly by planting more blossom trees including crab apple and almond.
"We're lucky that we have none of the usual predators as we are so high up. There are no foxes, squirrels, cats, rats or mice - but lots of insects and birds."
Round the corner, the Tudor garden will be planted with black and white plants to reflect the monochromatic scheme put in by Biba in the 1970s. Lewis has also chosen modern cultivars of plants that the Tudors would have used, including the purple-leaved Cercis canadensis 'Forest Pansy', Rosa 'Iceberg' and black and white tulips.
The Spanish garden is having a major overhaul - during HW 's visit a team from Kensington & Chelsea Mind was removing whole swathes of tired Wisteria from the pergola and getting the long bed ready for the new planting scheme.
"We're imagining how it would have been in 1958 - when Ralph Hancock's design would have reached maturity. He was at the forefront of design so he would have been 'out there'. We're going to use bright coloured plants like Canna 'Russian Red' and Cistus 'Sunset', plus architectural plants, and will paint the walls terracotta," says Lewis.
"It's been hectic since I started last April," he adds. "The renovation project started almost immediately, and I've been in discussions on planning with English Heritage and Kensington Council as well as working with landscape architecture practice Randle Siddeley Associates and historians on the project. It's been a steep learning curve."
He explains the challenges of working at this height: "Normally, plants or equipment are brought up in the lift, but cranes have been hired for this project."
Lewis and the gardening team also have to work around the many functions that are held in the gardens. It's certainly not your typical gardening job - what other roles would include sourcing a pair of flamingos? "It took me nine months to find them and I now know far more about birds than I ever thought I'd need to know," Lewis says.
Part of the appeal of this job, he says, is the fact that every day is different, and working for a successful commercial enterprise guarantees both a healthy budget and a can-do attitude.
"I've learned not to be scared. I'm happy now to argue my case concerning decisions about the garden and can explain why we should do it that way. And that's something to do with working for Virgin - the company demands that you put all your effort in."
Having trained as a garden designer while working full-time in advertising, it seems that Lewis is also a good deal for Virgin - a head gardener with a creative streak and a considerable amount of get-up and go.
Perhaps in recognition of this, he is currently working on designs for three gardens at Virgin's Moroccan hotel, the Kasbah Tamadot, set on a hillside at the base of the Atlas Mountains. As Virgin owns hotels all around the world, who knows what other design opportunities will open up for Lewis after the roof garden project is finished in April?
1988-91: Degree in Politics, City of London Polytechnic
1993-94: Postgraduate qualification in marketing and advertising, The
1991-99: Worked at various ad agencies
1997-99: BTEC National Diploma in garden design, Norwood Hall
1999: Silver medal for courtyard garden, RHS Chelsea Flower Show
2000-04: Trends predictor, Getty Images
2004: Sets up garden design practice
2006: Gardener, Kensington Roof Gardens
2006-08: Business development manager at Kensington & Chelsea Mind's
social enterprise Many Hands Trading
2008 to date: Head gardener, Kensington Roof Gardens