Analysis from Companies House shows that almost 14,000 new landlords were registered in the first five months of this year.
Last year, the number of registrations of new buy-to-let businesses reached a record high of 34,128, according to research by specialist insurer Just Landlords.
This was almost 70% higher than the five-year average of 23,549 per year.
Looking back further, Just Landlords finds that the annual number of registered buy-to-let companies has increased by 1,700% since the year 2000, when just 1,882 were established.
The pace of growth has accelerated sharply in recent years, with the 2020s already responsible for more new rental companies than in the entire period from 2000 to 2019.
Changes to mortgage interest deductibility, higher stamp duty costs and other regulatory changes are driving this trend.
The introduction of the 3% stamp duty surcharge on additional properties in April 2016 caused an immediate increase in incorporations, with registrations increasing by almost 59% over the following two years.
While London remains the largest market, accounting for almost a third of all registrations since 2000, the regional picture is shifting.
The capital’s share of annual registrations has declined in recent years, while growth is accelerating in the rest of the country.
The devolved nations have seen the most dramatic recent growth, with annual registrations in Scotland more than tripling since 2020 (+171%), while Northern Ireland (+148%) and Wales (+144%) follow closely.
Scotland now registers more than 2,100 new landlords per year, up from less than 400 in 2015.
Clark Ross, director of Just Landlords, said: “The scale of this shift is remarkable.
“We see clear evidence of the continued professionalisation of the private rental sector, with a growing number of landlords now operating through formal corporate structures.
“What is particularly interesting is that growth is no longer just concentrated in London.
“Some of the strongest increases have been seen in Scotland, the Midlands and Northern England, indicating that professional landlords are becoming an increasingly important part of the UK’s regional housing markets.
“There are a number of factors that could be driving this shift. London’s property values have long made it the dominant market, but the relatively lower entry costs in regional cities mean landlords can build a more diversified portfolio for the same initial outlay, potentially seeing higher returns.
“Rising house prices in the South have also pushed more renters into regional markets, increasing demand and making those areas more attractive to professional investors.”