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You don’t expect a tropical forest in deepest Camberwell, but Greg Smith’s garden is an amazing focal point of his redesigned home, and now part of the National Gardens Scheme, opening up to raise cash for charity.

Vice-president of international development at E & J Gallo Winery, Smith, 59, who travels the world, saw the lush green Bangkok garden of famous silk importer Jim Thompson, and decided he wanted his own version in SE5.

The towering, hospitable bloke brought up in Buffalo, US, takes the open day in his stride. “People come to visit the garden but I found one couple having a look round inside, even though they’re not supposed to.”

What look like palm trees are actually huge tree ferns, intensified by a carpet of the plant mind-your-own-business that seems greener than AstroTurf, and by a living wall down one side of the house.

Garden room: Greg Smith can enjoy his jungly garden all year from the glass “double box” framed in rusty Cor-ten steel built on to the back of his 19th-century home

To enjoy this all year, Smith built a big glass-walled living area — a sort of double box — on the back of the 1860s terrace house. From outside, the glowing orange rusty Cor-ten steel framing the extension makes a perfect foil to the green.

While he was at it, Smith deepened the existing basement six feet to give better height because he used to bang his head, making three rooms including a cosy television room. He went up into the roof, too. Lining out the sloping eaves made a tent-shaped room, plus en suite. This all created extra space for when his girlfriend Jeannette Bannister’s children come to stay.

Inside the bright new living space, the sleek, modern finishes include pale oak floors, glossy white lacquer and a white Corian-topped central island. Smith’s collection of Asian sculpture counterpoints Barcelona chairs and a wood-burning stove.

Walking through the more conventional front parts of the house, all now carefully restored, it’s like walking into a fresh take on a Victorian fernery. The light, affected by the giant plants outside, is extraordinary.

Sleek, modern finishes: pale oak floors and glossy white lacquer are easy to live with

In the remainder of the house, Smith has restored and replaced elaborate cornices, sorted out the mahogany stair rail, and generally taken great pains. On the ground floor, he opened up the two front rooms to make a double drawing room with high ceilings and talking-point chandeliers. “They were in Argentina and we had some air miles, so we went and got them.”

London fireplace specialists Chesney’s copied an existing marble fireplace for him, and he added a mix of modern furnishings and wooden antiques. The space can take their size, and Smith likes wood. A Victorian copy of a Renaissance buffet looks good in this space, but like other beautiful wooden pieces, some fruitwood, some marquetry, he says, “these days, few people want this stuff”.

Upstairs, the master bedroom is a charming pale green with bespoke figured silk curtains and antique furniture. The overall effect is a happy mix of new and old.

But buying a house was difficult. As a US citizen, Smith couldn’t get a mortgage for years. He arrived in the Eighties and rented a cottage in King’s Road that was “cute as hell”. To buy, however, he was required to put down 50 per cent in cash. “I just couldn’t afford it then.” He kept saving, but prices kept rising.

You’d never guess: the traditional brick façade of the terrace house keeps the secret of the ferny haven at the back

Finally, in 2002, he got the financing, and went straight online to find a house within his budget. He’d never been to Camberwell, but the tired house he saw, carved up and untouched since the Sixties, its walls nicotine brown, with a knackered kitchen on the back, offered more per square foot than anything else, so he bought it — even though a steel roof beam had been sawn right through, and the house seemed only to be standing through willpower.

At which point, Smith was transferred back to America. His friend Patrick de Nangle looked after the place while he was away and started off the fern garden, armed with a photo Smith sent him of Jim Thompson’s garden in Bangkok. Gallo brought Smith back in 2011, when he looked for an architect.

“I used Homes & Property. I made a list of 10 and whittled them down to four.” Tim Murray of Moxon Architects took him to see a project the practice had done for TV presenter Trinny Woodall.

Murray had a pre-planning chat with the planners, who approved of the idea of a clean glass box right across the back. However, when the plans were submitted, the old planner had gone and the new one refused permission. Smith and his architect had to take this on the chin and come up with a fresh design. After negotiations, the current design went through.

It’s a good thing Greg Smith is a patient man, because after a full 18 months in planning, building works took a further 18 months. At one point, looking straight up through the floors because the boards were so bad, he wondered how the house was still standing. But after new steels, repairing, and repointing, it’s all in good shape.

While my back was turned: Greg Smith bought a house — then his company sent him abroad for years. While he was away, the garden flourished in the care of a friend and Smith added to the planting - and restored and modernised the house - when he got back

Inside, Murray had great ideas, such as the white lacquered kitchen cupboards with long, cut-out lug handles, and a glass door dividing the old and new parts of the house.

This house is dramatic but also personal, and very nicely done, and the architect maximised what his client wanted. Looking out at the garden, it’s easy to forget you are in south London — not tropical Thailand.

WHAT IT COST

House was bought in 2002 for £450,000

Cost of works done: £500,000

Value now (estimate): £1.8 million

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Photographs: David Butler and Simon Kennedy