In London’s billionaires’ rows – especially those of the notorious lights-out variety, with houses whose owners rarely set foot in them – great security, like fashion and soft furnishings, is all about layering. It needs to work perfectly and seamlessly, but it needs to look good too and blend in with the décor. Take the handmade safes by the German company Stockinger, which can cost more than £100,000 and come in any colour you like, with customised handles and interiors.

The sky’s the limit when it comes to how much the wealthiest home owners will pay for peace of mind. Beatrice Knight at DDRE Global is handling a neo­classical mansion on the Wentworth Estate in Surrey that rents out for £12,500 a night – and whose owners have spent £500,000 on “security and additional supporting technology”.

In high-priced townhouses, “a dedicated staff and security wing at the point of entry often sets the scene,” comments Adam Arya, co-founder of Arya Douge architects. “From there, protection becomes almost invisible – carefully planned circulation, controlled sightlines, and spaces that allow the house to be monitored without ever feeling surveilled.”

One Hyde Park and The Knightsbridge Apartments – where huge flats have recently sold for £18 million and £11 million respectively – are hailed as the bullet-proof benchmarks for top-notch security.

“Biometric entry systems and hidden entrances that allow residents to come and go unseen give buyers the kind of reassurance they want,” says Harrods Estates director Shaun Drummond.

The personnel

And while the owners may rarely be in residence, there are year-round live-in staff. “No amount of technology”, says Joanna Cocking, head of Hamptons Private Office, “can replace a human monitoring system. The most valued layer of protection is trusted, long-standing staff.”

In a growing number of cases, there will be some lone teenagers in residence too, bringing extra security problems. “The non-dom exodus has split households’ living locations, and often the children are left in London for education. That has heightened the requirement for top-level close-protection security,” says Harry Dawes, founder of the prime buying agency Dawes London.

“The nannies and children will have one security detail, while the parents have individual protection. Annexed accommodation for security and household staff is a key requirement on clients’ briefs.”

Ex-military or special forces professionals can be found guarding huge houses all over London – and patrolling certain Kensington streets, where they will walk residents to their doors in safety. Expect to pay about £3,500 a week for their services, reports Simmi Sangha at Eccord, a super-prime management company in London. “But that cost is not ridiculous when weighed against the value of the property, its contents and, crucially, the peace of mind it brings,” she adds.

On arguably the best street in nearby St John’s Wood, protection comes with sartorial style too. At 52 Avenue Road – a new development of 12 stucco villas priced from £22 million and inspired by John Nash’s Regent’s Park mansions – ex-British Army Gurkhas will be on guard, bedecked in bespoke uniforms.

The Gurkhas form what Jon O’Brien, founder of the project’s developers, Domvs London, calls “the frontline physical protection layer”.