IN 2018, I began a longitudinal study, in which I’d call up luxury London estate agents, pretend to represent a well-known billionaire and go to house viewings on their behalf.

What I found was an “impossible city,” one that sits somewhere out of sight yet oversees our lives.

It’s not a particularly difficult undertaking. Swiftness is key; just pick up the phone (never leave an email, else you’ll be inundated with marketing), call one of the major luxury agents and arrange a viewing.

The more expensive, the more hoops you’ll have to jump through, so have a backstory pre-prepared; what does your billionaire boss do? Why does he need you specifically? Where else is he/she looking? It’s also vital to omit “ums,” “likes” and “ers” — you must sound professional, as if you’ve been doing this all day.

Once the viewing is arranged, don something both unequivocally smart and unequivocally boring; you want to look like you belong, but not as if you’re overcompensating.

And bring a video camera; this way you can tell the agent that the client trusts only film, and not just any promotional film, but your own unbiased one.

This they tend to shrug off; the super-rich and their assistants are, more often than not, decidedly odd. The agent has almost certainly dealt with stranger things.

The first thing you’ll notice once inside the “impossible city” is the simulacrum. Often, you’ll be guided into a show flat. This is an exact replica of a high-end apartment, only at the back of an office.

I was introduced to a show flat by a young intern on his first day. It’s a Narnia-esque experience; one moment you’re in a Knightsbridge office lobby, the next you stand alone, surrounded by the trappings of luxury — or rather, what the agents assume luxury should resemble.

Everything retains the aura of high-end living, but that’s all it is, an aura: expensive-framed photographs of stock-image families, untouched copies of F Scott Fitzgerald’s The Last Tycoon placed languidly on the shelves, plastic plants and an inbuilt sound system murmuring Vivaldi on repeat.

Properties surpassing the £30 million mark are an altogether more hurried experience. A chaperone will be insisted upon, and on some occasions you’ll be forced to hand in your phone at the door.

One of the properties I visited was, at the time, accommodating a Qatari family whose names I can’t disclose. According to the agent it was a family of five with two small children, but you’d never have known; no toys in the children’s rooms, no family photographs, no vital signs whatsoever.

Many of the apartments I visited on my trips to the impossible city, were situated in Eaton Square, SW1.

I remember the estate agent, as we trekked from flat to flat under the midsummer sun, jokingly dubbing the area “Red Square” on account of all the Russian investment.

The House of Saud also owns various properties in the area, but Red Square stays to this day dominated by the Russian oligarchy.

One Red Square property, a £15 million grade II listed home, owned by Russian mogul Andrey Goncharenko, was squatted by Autonomous Nation of Anarchist Libertarians (Anal) in 2017, resulting in a two consecutive sieges: first by neonazis, then by a private security company called The Sheriff’s Office — only the latter was successful. Anal withstood the far-right onslaught using fire extinguishers.

Another thing you’ll notice is the paranoia. Residents of the impossible city have been infected with a crippling distrust of the world. The more money they make, the more insecure they become about losing it.

The symptoms are readily obvious in the underground parking entrances and panic rooms (many of which are painted yellow — the oppressive colour of Charlotte Perkins Gilman’s wallpaper).

It becomes instantly obvious quite how paranoid the super-rich have become; almost all the high-end flats I visited in the impossible city had at least two exit points, with alarm buttons in most rooms.

A major player in London’s luxury property are the Candy brothers.

Though I was never formally introduced to Candy representatives on my visits to their Knightsbridge developments, I couldn’t help but notice their comically villainous titles in the hushed small talk of estate agents.

“The Candies” (Christian and Nick Candy) are British-Cypriot luxury property moguls with long-standing ties to various authoritarian governments.

Though the Candies operate independent businesses, their crowning achievement came in 2004, when Candy and Candy demolished the 50-year-old Bowater House in Knightsbridge to build One Hyde Park — which now houses Rolex, McLaren Automatic, Abu Dhabi Islamic Bank and 86 luxury apartments — whose flats are listed as secondary homes by three-quarters of its tenants.

One Hyde Park was the hardest property to infiltrate.

Proof of annual income was demanded of me, and my fake name was run through the database so as to make sure I didn’t show up on record as a poser. To circumvent this rigorous vetting, I had to go so far as to enlist the help of a company executive who agreed to let me use his proof of income.

Once inside the vast, postmodernist complex, I was apprehended by three large, hot-headed security guards who insisted on confiscating my SD card before letting me through (luckily, they didn’t know much about cameras, and only took one of the two).

The penthouse itself was at once luxurious and soulless, wealth-ridden yet culturally bare. Here, high above the world, in the motion-lit hallways of the multi-storey penthouses, do you realise that these are not homes, not houses, they are residential vaults, mineral deposits, existing only to accrue value.

Though, legally speaking, the Candy brothers have not formally broken the law, they have serious blemishes in their moral record.

In 2017, they narrowly won a high-profile litigation against property developer Mark Holyoake, who claimed they used threats against his family to extort avaricious repayments on a loan.

Allegedly, the Candies offered to pass Holyoake’s details to Russian debt collectors “who would not think twice about seriously fucking hurting you…”

Christian Candy’s mentality is also neatly summated in his statement on the British psyche after the financial crash: “The British psyche in this country is very much towards a sort of jealousy towards success … there’s a sort of a jealous culture developed by the media.

“In America, there’s the American Dream, the guy in Harlem that sees a nice car and says I’d love to have a car like that … Here in the UK, if that same car was in Brixton, the guy looking at the car would say I wanna key it…”

The impossible city is not a community, not a residence, but something else — one of the few commodities, aside from art and gold, that never decreases in value.

Our capital is not a strongroom, nor should it be treated as such. Make no mistake, London has always played host to extreme wealth, but it isn’t until a few decades ago that the city has seen this enormous rise in foreign dark money investment for property.

There were the Greek shipping tycoons of the ’70s and ’80s, and now, in much larger clusters, Russia, Qatar and Saudi Arabia. All pandered to by the likes of short-fingered developers like the Candies.

The government must to make it more difficult for overseas companies to use offshore businesses to invest in London property without living in it. We need to crack down on the impossible city and its hidden wealth.

Many developers will end up giving you a tour of the architectural miniature. There are two categories of buildings on a miniature: opaque and transparent.

Opaque buildings will be left as they are, or are soon to be completed. Transparent often signifies forthcoming demolition. When I was shown the miniature, in the borough of Kensington and Chelsea, where wealth disparity is among the highest in Europe, a third of the properties were see-through.

Grenfell, absent from the model, loomed, still charred, less than a mile away.