The Sunday Telegraph reported that the taxman will send 40,000 letters over the next four months asking the recipient to arrange their affairs or risk receiving a large fine or criminal investigation.
Approximately 5,000 landlords have been sent the letters and a 30-day window to respond has been given.
Accountants have said that in the past year HMRC’s approach has toughened. It is understood that more people have been deployed to hunt down £500m underpaid each year.
Last October, a campaign to encourage landlords to come clean was launched by the taxman and accountants said that ten months on from the launch the Revenue has begun gathering information from a wider range of sources.
Mark Giddens, a partner at UHY Hacker Young, told The Sunday Telegraph: “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.
“The housing benefit payments that go direct to landlords are also being monitored more closely. This information can be obtained through the local council’s records.
“By investing all this time and effort they have certainty stepped up the pressure on landlords who are not declaring enough, and the letters are the next part of that.”
Lucy Brennan, a partner at Saffery Champness, told The Sunday Telegraph: “Those who let out a holiday home will not be 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.”
A spokesman for HMRC said the campaign website has had hundreds of thousands of visits but refused to disclose how many landlords have come forward since the launch.
