Campaigning charity Shelter claims around one in 10 landlords quit the lettings sector each year.
Using new research by YouGov it says there is substantial churn in the sector annually.
In a new blog Shelter spokesman John Bibby says a survey of almost 4,500 people has found that seven per cent of British adults have been a landlord before, but are not now - it says that is the the equivalent of around 3.5m ex-landlords.
About 29 per cent of these have stopped being landlords in the five years to March 2017, equivalent to almost a million people and an average of almost 200,000 a year – at least 10 per cent of the number thought to be landlords at the moment.
“Of course, the fact that the total number of landlords has continued to increase, even while a large number of landlords have been leaving the market every year, means that even more people are starting to let out property every year” says Bibby.
The charity has also looked at data from HMRC showing that the number of tax-paying landlords in the UK went up by almost half a million in the five years to 2014/15, to take the total to more than 1.8m.
Shelter claims this figure is an underestimate, claiming on the blog that “some landlords evade tax by not declaring their rental income and others own their properties through company structures.”
By using that data, even so, the charity suggests this indicates that while around 200,000 landlords have stopped being landlords every year, they have been more than replaced by 250,000 to 350,000 people who have started becoming landlords every year.
The charity says finding out churn in the sector is important because landlords selling their properties is an indicator of evictions.