HMRC is set to contact thousands of landlords it suspects of not paying enough tax.
Letters will be delivered to 40,000 landlords over the next four months. Recipients will be warned that they risk a fine or criminal investigation if they do not contact HMRC to put their affairs in order, with a 30-day window in which to respond.
The government is thought to be losing £500 million in tax revenue every year as a result of underpayment. Tens of thousands of landlords are believed to be bending or breaking the rules by failing to pay income tax on their rental receipts and capital gains duties on second properties.
Mark Giddens, a partner at accounting and auditing firm UHY Hacker Young, told the Telegraph that HMRC has recently stepped up its efforts, broadening its enquiries beyond the Land Registry and the electoral roll.
"It was not until April this year that the taxman sent out notices to letting agents in which they asked for details to be provided of everyone on their books," he said.
"The housing benefit payments that go direct to landlords are also being monitored more closely."
HMRC's determination to use every resource at its disposal to find tax evaders also appears to extend to social media.
Lucy Brennan, a partner at chartered accountants Saffery Champness, said this approach is proving useful in instances such as holiday homes being let out by people who are not registered to vote at that address.
"The Revenue has increasingly been using social media to look into cases where a holiday home is, for instance, being advertised to friends, to ensure that the right amount of tax is being declared on that property," said Ms Brennan.
HMRC estimates that about 1.5 million landlords are currently operating in Britain, even though fewer than 500,000 taxpayers are registered as owning second properties.
The tax authority is currently running the Let Property campaign, which offers tax tutorials and gives landlords the opportunity to bring their affairs up to date.
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