Residential landlords are being targeted by Her Majesty’s Revenue and Customs (HMRC) over unpaid taxes.
It has been estimated that around £500m could be owed by up to 1.4m private buy-to-let landlords in the UK.
There are currently fewer than 500,000 taxpayers registered as owning a property other than their main home.
HMRC believes some landlords may have made honest mistakes about their tax liabilities but are issuing a warning that ignorance is now no longer an excuse.
Marian Wilson, head of HMRC campaigns said: “All rent from letting out a residential property or holiday home has to be declared for income tax purposes.
“We appreciate some people will have made honest mistakes, and some may not be fully aware that the rent from a property is taxable, and that is why it always makes sense to talk to us so we can help.
“It is always cheaper to come forward voluntarily and pay the tax you owe, rather than wait for HMRC to come calling.
“Telling HMRC about your tax liabilities is simple and straightforward, and help, advice and support are available.
“The message for all landlords owing tax is simple; it is better to come to us before we come to you.”
Failure by landlords to declare their taxable income could result in criminal proceedings.