Residential Landlords Association: https://www.rla.org.uk/

National Landlords Association: http://www.landlords.org.uk/

Gov.uk information for landlords: https://www.gov.uk/browse/housing-local-services/landlords

Rent Smart Wales: https://www.rentsmart.gov.wales/en/

ARLA propertymark: http://www.arla.co.uk/

UK Association of Letting Agents: http://www.ukala.org.uk/

The Guild of Residential Landlords: http://www.landlordsguild.com/