For someone who could soon have more than £100m sloshing around in his bank account, Fergus Wilson appears to have remarkably little interest in his money. “We are always getting letters to invest in this, that or the other, like buying a private jet,” says Fergus, 61. “But what do I want a private jet for? I never go anywhere.”

A stately home? A villa in the south of France? A luxury yacht, perhaps? Fergus, who together with his wife, Judith, 59, has spent the past decade and a half amassing a portfolio of 700 investment properties, looks nonplussed. “We’re not that kind of folk,” he says. “We’re pretty basic people.”

After a pause, Judith concedes that she might fancy a cruise — although neither of them likes the heat, and Fergus gets restless on long journeys. But, yes, they could buy a couple of farms on top of the two they own already, or add to their collection of racehorses.

Britain’s best-known buy-to-let landlords may seem unfazed by the prospect of their impending enrichment, but their announcement earlier this month of plans to liquidate their entire portfolio is attracting interest from some most unlikely quarters.

Fergus says several Russian buyers have emerged as frontrunners to buy all 700, for which they want £175m-£180m. “How serious they are, I don’t know,” he says. “There’s also a Bulgarian, a Saudi,one from China, one from Japan and one from India. We’re just sitting back and waiting to see who comes forward.” Realistically, any such buyer is going to demand a discount, but with borrowing of “only” £45m, the couple should be left with well over £100m, even after they have paid off their taxes.

“It’s only if we were unable to sell in bulk that we would consider selling one at a time,” Fergus says. “But that would be the last resort.” In fact, it seems unlikely to come to that: interest from institutional buyers means they should be able to sell the properties in blocks of at least 10, which means their tenants will be able to remain.

While the buy-to-let sector has been transformed in the public perception, in the space of a couple of years, from infallible get-rich-quick scheme to a licence to lose money, the Wilsons have shown everyone else how it should be done. The former maths teachers, who live in a £2m house they built for themselves in 60 acres south of Maidstone, Kent, acquired their first taste of the money to be made in property as students in the mid-1970s. They discovered that they could pay the rent on their top-floor flat in Blackheath, southeast London, by taking the whole house and subletting the three floors below. Then, in 1975, they bought their first home, a three-bedroom house on the outskirts of Maidstone, for £8,200.

A decade later, they embarked on a course that was to turn them into multimillionaires. When they bought another house a few doors away in 1986, they kept the old one and let it out — and found the rent more than covered the mortgage on their new home.

In the years that followed, helped by falling interest rates and banks desperate to lend, the couple, who had by then both given up their teaching jobs, embarked on a remarkable spending spree: in 2003, their peak year, they bought 350 homes. Their final purchase, last June, was of two houses in Ashford.

In a sense, the Wilsons were doing what countless other buy-to-let investors did, albeit on a much larger scale. Yet that is to belittle the scale of their achievement — and doesn’t explain why they have prospered while others have crashed and burned.

The couple followed several simple self-imposed rules. First, they kept it local: their properties are all within 40 minutes’ drive of their Kent home — 200 of them in and around Maidstone, 320 or so in Ashford and about 60 in Hawkinge, near Folkestone, where they bought an entire road of 15 homes. “Every town has the right side of the tracks and the wrong side of the tracks,” Fergus says. “It’s a matter of local knowledge.”

Important, too, was the type of property. Although they initially bought flats (and still have 30), they realised houses were a better bet: not four-and five-bedroom detached ones, but two-and three-bedroom terraces and semis.

The building — and subsequent upgrading — of the Channel Tunnel rail link lifted prices in Ashford, where some of the trains stop. A further boost is expected when the high-speed domestic rail service from the town goes fully operational in December.

This strategy has spared them the woes of amateur investors seduced into buying off-plan flats in city-centre blocks, which plunged in value even before they were completed — leaving the owners in instant negative equity.

The Wilsons’ portfolio has not been immune to the falling market — although the prices of houses have held up better than flats — but the recession has brought other compensations. At £80,000, the monthly bill on their hundreds of interest-only mortgages is still enough, says Fergus, “to give many people a heart attack” — but, thanks to the sharp fall in the Bank rate over the past 12 months, it is a fraction of what it was a year ago, and covered several times over by gross rents of £600,000. “If the interest rate had gone up rather than down, it would have been a disaster,” he says.

So why stop now? Managing the properties is a full-time job, despite a staff of 14, most of them responsible for maintenance. And with neither of their thirtysomething daughters keen to take their place, the Wilsons have been intending for some time to sell up.

The initial plan was to do so gradually, but that changed in spring last year, with a simplification of the rules concerning capital-gains tax, which meant they could liquidate their entire portfolio without effectively being penalised. Unfortunately, the climate was so bad that nobody wanted to buy. With the recent upturn, that has changed, and the couple are confident of selling.

In the meantime, £100m or no £100m, they are struggling to contemplate life without their empire. “We have very much enjoyed what we’ve been doing,” Fergus says. “It’s been a labour of love. It’s like having a child that’s grown up. I shall miss it terribly.”

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