The Non-Resident Landlords (NRL) Scheme is a scheme for taxing the UK rental income of non-resident landlords.
The scheme requires UK letting agents to deduct basic rate tax from any rent they collect for non-resident landlords. If non-resident landlords don’t have UK letting agents acting for them, and the rent is more than £100 a week, their tenants must deduct the tax. When working out the amount to tax the letting agent/tenant can take off deductible expenses.
Letting agents and/or tenants don’t have to deduct tax if HM Revenue & Customs (HMRC) tells them not to HMRC will tell an agent/tenant not to deduct tax if non-resident landlords have successfully applied for approval to receive rents with no tax deducted. But even though the rent may be paid with no tax deducted, it remains liable to UK tax. So non-resident landlords must include it in any tax return HMRC sends them.
source:http://www.hmrc.gov.uk/international/nr-landlords.htm