With the help of letting agents, the taxman has recovered over £20m in unpaid tax from private landlords.

Last year, hundreds of letting agents were sent statutory notices to provide details of rents collected on behalf of all landlords.

Figures released this week by HMRC show over £20m recovered as at the end of January – massively up from the figure of £7.9m announced in October.

HMRC’s Let Property Campaign is an ongoing crackdown on private landlords with undisclosed rental income.

The campaign provides buy-to-let and other private landlords with an opportunity to make a full and voluntary disclosure on more favourable terms than if they were caught.

It is understood that over 9,500 landlords have so far taken up the opportunity to bring their tax affairs up to date.

Ian Leigh, tax partner at accountancy firm Jefferys Henry LLP, said: “These figures should come as a warning to anyone with undisclosed rental income.

“With increased data-gathering activities, it is less likely a case of if and more likely when HMRC catches up with you.”

HMRC now gathers information from much wider sources beyond local authorities, the Land Registry and electoral roll, and now includes agents.

Leigh said: “Landlords with undisclosed rental income should take this opportunity to come forward and regularise their tax affairs as soon as possible.

“Penalties as low as 20% and affordable payment plans can often be negotiated for those who make a voluntary declaration as part of the Let Property Campaign.”

Landlords who ignore this opportunity face penalties of up to 100% and in certain cases criminal prosecutions.

Earlier this year, two men from London and Essex were arrested as part of an investigation into an alleged Capital Gains Tax and Income Tax fraud.

HMRC claims the pair had failed to declare CGT on a number of properties that they had bought and sold.