Historically, local authorities have run voluntary registration schemes for HMO landlords, which have been easily avoided.
Amazon will target landlord bodies, such as the National Landlords' Association, and relevant service providers such as mortgage lenders, through trade press and local media.
The definition of an HMO was set in the Housing Act 2004 as a property in which three or more unrelated people live. However, the mandatory licence applies to larger dwellings, where five or more non-family members live over three floors or more.
The licence sets minimum standards for letting and aims to end bad practice such as harassment of tenants.
Amazon prevailed against Blue Rubicon and Grayling to win the brief.
For more details go to www.propertylicence.gov.uk.