The number of landlords has fallen over the last two years – although there has been a rise in supply of homes available to rent.
Research by Countrywide found that the number of landlords peaked at 3.72m in 2015.
This year, there are 154,000 fewer landlords but the number of rental homes has risen from 4.9m to 5.1m.
Countrywide estimates there are now 3.56m landlords in total, with the average landlord portfolio the biggest since Countrywide’s records began in 2005.
The average landlord owns 1.44 rented homes in 2017, up from 1.33 in 2015. However, the large majority of landlords (73%) own just one buy-to-let property.
Average rents for new lets rose to £954 pcm in August, up 1.6% on the same time last year, according to Counrywide.
Research director Johnny Morris said: “The increasing number of rented homes is being driven by landlords expanding their portfolios rather than new landlords entering the market.
“Increasing regulation in the sector accompanied by recent changes to income tax relief on mortgage interest payments seem to be favouring more experienced, professional landlords.
“Despite expanding portfolio sizes, the sector is still characterised by those owning just one or two homes.”