Liverpool City Council has a Landlord Licensing Scheme that all leaseholders who wish to rent out their apartment must register with.
Further details are available from the LCC website:
Some organisations that will support both tenants and landlords:
ARLA The Association of Residential Lettings Agents
The National Approved Letting Scheme
Residential Landlords Association
Articles about renting and tenancies:
London Council Launches Lettings Agency for Private Renters The Guardian 10.03.16