In a bid to clamp down on private landlords who evade tax due on their rental income or from the sale of a buy-to-let property, HM Revenue & Customs has launched 40 specialist taskforces to target cheats in the buy-to-let sector, according to The Overseas Guides Company.

The taxman expects to recover $4m in unpaid tax from the South East region alone, while in Yorkshire this has led to 12 cases of landlords being criminally investigated.

Recent reports also showed that an increasing number of new developments in London are bought by expats wanting the security of a buy-to-let back in the UK.

HMRC is giving all buy-to-let investors until the 6th September this year to voluntarily disclose and pay any unpaid tax resulting from the sale of a second home.

It says that once this deadline passes, tax experts can expect an aggressive attack on undeclared rental income.

Recent research by a London accountancy firm showed that buy-to-let landlords paid £2.02bn income tax on their rental income in 2010-11, up 13% from £1.78bn the year before.

It also revealed that the number of Britons with direct investments in let property increased from 1.8 million in 2009-10 to 1.9 million in 2010-11.

There is concern that many expat landlords might not fully comprehend their tax reporting obligations in the UK.

Measures to minimise lost rental revenue are already in place. The Non-Resident Landlord Scheme (NRLS) requires UK letting agents to deduct basic rate tax (20%) from any rent they collect.

And if the non-resident landlord does not have an agent acting for them, and the rent surpasses a minimum amount, then their tenants must deduct the basic rate tax themselves.

Expat landlords are being advised to seek advice from an adviser who specialises in expat affairs to minimise the risk of falling foul of the taxman.