Longman Dictionary of Contemporary English
sitting tenant
noun
EXAMPLES FROM CORPUS
▪ A sitting tenant who came with the greenhouses ... and is doing his bit to keep down the slugs.
▪ Like these events in Knowsley North, where the sitting tenant is George Howarth.
Wikipedia
Sitting tenant
A sitting tenant is a tenant already in occupation of premises, especially when there is a change of owner. Sitting tenants can result from a failure to evict an assured shorthold tenant following a change of owner or where there is a protected tenancy. Where a landlord sells a property but fails to evict a tenant the new landlord is said to 'step in the shoes' of the old landlord and the terms of the tenancy continue.