NICKNAMED “God” by his fans, Robbie Fowler scored 183 goals for Liverpool Football Club. But his career as a property magnate may have been even more successful. As he banged in the goals, fans chanted, to the tune of “Yellow Submarine”, “We all live in a Robbie Fowler house.” Mr Fowler has since hung up his boots and is now the face of the Robbie Fowler Property Academy, which offers seminars on how to make it big in housing. With what is believed to be a portfolio of over 50 properties, his fortune may run into the tens of millions of pounds.

Plenty of Britons want to emulate Mr Fowler. In the past two decades they have piled into the “buy-to-let” market, acquiring homes to rent out. These days one in 30 adults—and around one in four MPs—is a landlord. Roughly a third of them are retired, many having turned to the housing market as the returns on their savings dwindled. The rent from buy-to-let properties, which we estimate at £55bn-65bn ($73bn-87bn) a year, is equivalent to the salary bill for the financial and insurance industries, in which over 1m people work.

The buy-to-let phenomenon got going in 1996, with the introduction of mortgages which no longer required the borrower to live in the house they were buying, says Lawrence Bowles of Savills, a property firm. The years since then have seen frenzied growth (see chart). Investing in the housing market has seemed like a one-way bet, with prices trending upwards in real terms for four decades, mainly because government after government has failed to loosen planning restrictions on building new houses. Now, however, there are signs that regulatory changes have begun to send the buy-to-let boom into reverse. That is bad news for Mr Fowler’s disciples, but there could be benefits, too.

The growth of the rental market is not in itself an unwelcome trend. As the supply of places to let rises, the cost of renting falls. Though many tenants may prefer to own their home, others like the flexibility of renting. If workers can up sticks easily, they are likelier to find work that suits their skills. That is good for productivity growth. Yet the buy-to-let boom also has its downsides. Like the gentry of old, Britain’s new class of landlords is often amateurish. Most operate on a very small scale: six in ten have just one property. And many seem to manage their houses poorly. Almost 30% of private-rented dwellings are officially classed as “non-decent”, meaning that they fail to meet basic standards for things such as heating or their state of repair. (By contrast, 15% of council housing is in such a condition.) Young folk who would prefer to own a house than pay rent to their elders complain that the buy-to-let boom is one of the great injustices of modern Britain. The Conservative Party is worried. Over half of private renters voted for Jeremy Corbyn’s Labour Party at the general election in June, a higher share of private renters than voted for Tony Blair when he won by a landslide in 1997. Life has lately become harder for landlords. In 2016 the government raised stamp duty, a tax on homebuyers, by three percentage points for those buying second homes, including buy-to-let properties. It abolished a generous “wear and tear” allowance for those letting furnished properties, and in April began tightening the rules on how landlords write off interest costs against income tax. These changes are enough to turn healthy annual profits into losses, especially for investors in higher tax brackets and with large mortgages.

Meanwhile, yields on rental properties have fallen. House prices have risen faster than rents, in part because buy-to-letters have increased the demand for properties available for purchase, while simultaneously increasing the supply of places to rent. Britain’s ratio of house prices to rents is now 50% above its long-run average. All this makes buy-to-let investment less lucrative. Data from the Bank of England suggest that yields in September were below 5%, their joint-lowest rate since records began in 2001, when they were above 7.5%.

At a recent seminar of the Robbie Fowler Property Academy in a nondescript hotel in London, the mood remained upbeat. Mr Fowler claims in a promotional video that, “It doesn’t matter what state the market’s in—there’s always money to be made.” Yet few are so optimistic. In the third quarter of 2017, new buy-to-let lending for house purchases was around 15% below the average of the past five years. Research from Savills suggests that, for the first time, landlords may be selling up in large numbers.

One consequence could be a more stable financial system. Roughly 15% of mortgage debt is on buy-to-let properties. The Bank of England has warned of risks associated with this. Property investors buy when prices are rising but sell when they are falling, making house prices more volatile. Buy-to-let landlords are also more likely to default than owner-occupiers. One reason is that doing so does not force them out of their home. Another is that buy-to-let mortgages are more likely to be interest-only (ie, where the principal is not repaid), which means that monthly repayments can go up sharply if interest rates rise. The Bank of England’s stress tests last month showed that the rate at which landlords’ loans turn sour could be four times greater than the rate for owner-occupiers. All things considered, a smaller buy-to-let sector may come as a relief to regulators.

It might also cheer up would-be homeowners. Buy-to-letters sometimes compete with first-time buyers for property—and they often win, since they tend to have bigger incomes. Lately the buy-to-let boom has been correlated with galloping house prices, which have made it harder for youngsters to get a foot on the housing ladder. One study suggested that more than ten percentage points of the 150% rise in real house prices between 1996 and 2007 was caused by increased lending to landlords. As the buy-to-let market has turned, house-price growth has weakened. In July to September the number of mortgages granted to first-time buyers hit its highest level since 2007.

The future for buy-to-letters will not get much brighter. In January a tweak to the rules on taxing capital gains will increase the liabilities of landlords who register as businesses. Institutional investors are moving on to buy-to-letters’ turf, hoping to benefit from their economies of scale to offer better housing to tenants. It was good while it lasted, but the golden age of the amateur landlord may be over.