The proportion of "accidental" landlords has fallen annually for the first time in five years, according to analysis.
One in 14 (7.1%) homes coming on to the rental market across Britain this year so far had been listed for sale within the previous six months, the lowest level since 2015, according to estimates from Hamptons International.
This is the first fall in the proportion of homes let by accidental landlords since 2014, and down from 8.6% in 2018.
Hamptons said a slowing sales market has triggered some home owners to let their property instead of selling - meaning they become "accidental" landlords.
But it said that tax changes for landlords may have affected the situation as some could face increased bills.
Hamptons International said London is Britain's "accidental landlord capital".
So far this year, 10.1% of homes listed to rent in London had been up for sale during the previous six months - although this is down from 12.6% in 2018.
Aneisha Beveridge, head of research at Hamptons International, said: "Despite a weaker sales market, which tends to encourage accidental landlords, the proportion of homes to let having previously been listed for sale has fallen for the first time in five years."
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Those who do end up letting their properties out may find they can achieve higher rents due to a lack of choice for renters.
Ms Beveridge continued: "Rental growth remains steady in Great Britain, with the average cost of a newly-let property rising 1.8% year on year.
"Lower stock levels mean that the South continues to drive rental growth."
So far this year, 10.1% of homes listed to rent in London had been up for sale during the previous six months - although this is down from 12.6% in 2018
- London, 10.1%
- Wales, 8.0%
- North East, 7.8%
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- North West, 7.6%
- East of England, 6.2%
- South East, 6.0%
- South West, 5.8%
- West Midlands, 5.6%
- Scotland, 5.4%
- East Midlands, 5.3%
- Yorkshire and the Humber, 5.1%