The government is being encouraged to consider introducing a national register of rental properties to improve tax compliance in the buy-to-let sector.
Unscrupulous landlords have been accused of tax evasion which could cost the Treasury up to £1.73bn a year.
The accusation has been made by TaxWatch, which claims to be the UK's only charity dedicated to compliance and sound administration of the law in the field of taxation.
The new figures are revealed in a report by the think tank and suggests that levels of non-compliance have increased sharply over the past decade.
HMRC has long said that it is targeting tax evasion by buy-to-let landlords but it has failed to publish official figures on the scale of evasion in the PRS since 2010.
Alex Dunnagan, a researcher at TaxWatch, commented: “Not only is such a staggering amount being lost in tax to the private rented sector, HMRC isn’t even recording the true size of it.
“By any calculation, the amount uncollected today is far larger than what it was in 2010, despite the government claiming to be cracking down on landlord tax dodging.
“Introducing a national register of rental properties would be a simple means of improving compliance, and would raise large amounts of money for the government which is desperately needed at this time.”