When representatives of a young, wealthy Middle Eastern woman approached Tim Macpherson at the Mayfair office of estate agent Carter Jonas recently, he told them he had just the home for her: a period house costing more than £50m in one of London’s most upmarket areas.

The historic property had never had a For Sale sign outside nor been listed with any agent, though its owners had quietly informed Macpherson they wished to sell. You will not find its details or photographs online and the buyer went through a “hugely expensive exercise” to purchase it through a company structure that makes her own identity difficult to ascertain. She did not even visit the property until several of her entourage had been first.

The woman passed anti-money laundering checks and is not what regulators call a “politically exposed person” who may be vulnerable to corruption in their home country, Macpherson says. But her high-profile family means that protecting her identity is paramount.

Such off-market deals make up about 40 per cent of Macpherson’s business, which concerns itself with the UK capital’s most exclusive homes, mainly costing £10m or more. Many buyers in his market, he says, will not even consider a home that has at any point been listed for sale online.

Such discreet sales are often surrounded by further measures to maintain secrecy around a home and its residents. These range from ownership structures that obscure identity to state of the art alarm systems and staff who do not know when their employers will come or go. “People always keep their houses up and running, not as a matter of extravagance but because you can’t tell the staff: ‘I’ll be here a week on Thursday.’ Not even the household can know,” Macpherson says.

They don’t want any possibility that their children’s lives will be in any way disrupted

Secrecy has long been a top priority for many ultra-wealthy homebuyers and sellers. It has become more difficult to maintain, however, since the UK and other governments began taking measures to combat money laundering in the property sector. In June, the UK government began publishing a list of “beneficial owners” of companies, including those that own properties, in a move to prevent corporate wrappers from being used to hide real ownership.

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It has also signalled a tougher approach to those who use bricks and mortar to stash the proceeds of crime. The wife of the former chairman of a state-owned bank in Azerbaijan was in October revealed as the subject of the UK’s first unexplained wealth order after she acquired assets including an £11.5m house in Knightsbridge.

Unexplained wealth orders (UWO), which since January 2018 can be issued by the UK’s National Crime Agency, require the owners of assets worth £50,000 or more to explain how they were able to afford them when their declared income seems to be too low. The orders are aimed at those linked to crime or political corruption.

The UWO required Zamira Hajiyeva, 55, to explain to the NCA how she was able to afford the property — along with a £10.5m golf course she also owned. If she cannot, her properties could be seized, while her lawyers in October lost a legal attempt to prevent publication of her identity. The legal moves sent a chill through potential buyers of high-end London property who might struggle to explain the source of their wealth, according to one agent in the sector. Earlier, in 2013, authorities also cracked down on tax avoidance by introducing an annual levy for properties held within companies.

But crime and tax are not the only reasons why wealthy homebuyers want their identities to stay secret. The 2016 “Panama Papers” leak exposed a series of individuals who secretly owned properties through companies. Among them was Emma Watson, best known for her roles in the Harry Potter films, who had previously been forced to hire bodyguards after incidents involving stalkers.

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Her representative told the Spectator magazine that following the 2016 leak the UK citizen had “set up an offshore company for the sole purpose of protecting her anonymity and safety . . . [Her safety] has been jeopardised in the past owing to such information being publicly available . . . Emma receives absolutely no tax or monetary advantages from this offshore company whatsoever — only privacy.”

Off market is an effective way but not a cheap one because the seller holds the cards

Macpherson says that in other cases, an overseas buyer’s urge for secrecy “is driven by politics from their home region, or the fact that they may have had money out of their country of origin for decades, but now there are restrictions on moving money around in their home country because of a new political regime or tax”.

He adds: “In other cases they are English and it’s literally down to discretion. Their most prized possessions are in the house . . . and they don’t want any possibility that their children’s lives will be in any way disrupted.”

Another reason is a political environment where, with the rise of populism, focus on the wealth gap is growing, says Charles McDowell, a London agent who runs McDowell Properties. “People don’t want the whole world to know they are selling something for £40m . . . people spending a lot of money in this current climate are mindful of public opinion,” he says. Sales in Kensington Palace Gardens, a high-security street close to the Kensington Palace homes of princes William and Harry, where the average home costs £33m, are almost all off-market, McDowell says.

Timothy Davis, a veteran real estate broker with Corcoran in New York’s Hamptons area, says some buyers in the upmarket destination have similar concerns. “We are doing a deal now on the oceanfront where the buyer doesn’t want to be known. They’re not famous, they just don’t want to be known to have paid $20m to buy a house. In a time when there is sensitivity around whether people have too much money, you don’t want to be that guy.”

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Off-market remains the main way that homes are transacted in “seriously competitive” UK high-end country house sales, says Roarie Scarisbrick, a partner at the buying agency Property Vision. “The market around [London-bordering] Home Counties’ schools is ludicrously competitive and there are tales of life-long friendships being destroyed in fights over houses.”

But Scarisbrick believes off-market selling often favours sellers over buyers in financial terms: in addition to seeking privacy, sellers may choose this way to obscure price changes and comparisons.

Buyers may believe they are getting a good deal but, he says: “Off-market deals are a symptom of a bull market — [buyers] want the clearest route to buying a property for fear that the next one is going to cost 10 per cent more.

“It has become this sort of mystical idea that the best houses exist in the off-market space. But my advice to buyers in those conditions is actually to hold and wait to spend a bit of time in the open market. [Off market is] an effective way of buying property but not a cheap way because the seller holds the cards and has the back-up of the open market if you don’t dance to their tune.”

Prime London property has not been rising for three years: along with prime property markets in other global cities, it is undergoing price falls and low transaction levels. Yet the mystique of the off-market purchase is growing for another reason: a desire to transact away from the unforgiving eye of the internet, where buyers can easily find signs of price cuts or long periods when the property is up for sale.

That is the thinking behind a start-up operating in the London area of Fulham. Invisible Homes sounds like a contradiction in terms: an online market for off-market homes. But it keeps records out of the public domain and, like a dating site, it only sends buyers details of a property once the system has matched buyer with seller and the seller has decided to make contact.

Mark Wells, its founder, says off-market transactions have so far remained “analogue”, even as other home sales have moved to online portals. His system, he believes, prevents properties becoming “stale” when they spend a longer time on the market. The site does not carry homes that are listed elsewhere: exclusivity is key to its offering for buyers, he said.

Wells is not the only entrepreneur pursuing the idea of sales that are online, yet off-market. Compass, the US home listings site, also has an off-market section. Mauricio Umansky, founder of the California-based real estate brokerage The Agency, who has handled homes owned by singers Michael Jackson and Prince, and former basketball player Michael Jordan, last year backed the launch of ThePLS.com, an off-market listings site aimed at brokers. Umansky is currently offering a $60m off-market beachfront property in Mexico.

Davis notes that US property owners can still keep their identities secret by using a limited liability company registered in a state that does not reveal ownership information. Such measures, together with off-market purchases known in the region as “whisper listings”, are key to Los Angeles real estate, where celebrities play cat and mouse with photographers and the press.

In the Hamptons, says Davis, it is mainly overseas buyers who seek off-market homes, particularly those who are already accustomed to secret deals or who come from locations where crime rates are high, teaching them to “look over their shoulder more”.

He, too, is sceptical of the off-market phenomenon, which he says is comparatively rare on his patch: “It’s a smoke and mirrors thing . . . there’s something good about a market which is a bit more public. You have a way of gauging if it’s the right or wrong time to buy. [A high level of off-market deals] takes the energy out of the market.”

However, the internet age has increased some wealthy homebuyers’ urge for secrecy, as they seek to avoid digital invasions as well as physical ones. A well-used feature on Google Street View enables householders to request that their homes are blurred out. Homes, such as that of Facebook founder Mark Zuckerberg, become invisible.

If Wells and his competitors are right, technology can maintain privacy while making secret home transactions more efficient, cheaper and more widely available. While Wells’ site regularly handles multimillion-pound deals, the traditional territory of off-market sales, he says owners of less expensive properties are also using the site to quietly sell their homes. Currently, Invisible Homes is offering two former social homes for about £500,000 each.

Wells says: “The benefits of off-market selling used to be limited to the super-rich: we’ll make it available to the guy with a property for £100,000.”