If I have found that my tenant has sub-let my property to some other person without my consent, then what can I do to protect my interests?

A tenancy document usually contains a clause that prohibits the tenant from subletting the property to another party. Any subletting by the tenant will be a breach of such a clause and the landlord can institute legal action for compensation.

If the tenancy document does not contain a clause that prohibits subletting, then the mere act of subletting, even without the landlord’s consent, may not be illegal. As a tenancy has the effect of passing the landlord’s interests in the property to the tenant, the tenant may deal with the property in whatever manner (except for any illegal activities or actions which would violate the tenancy document) within the period of the tenancy, including subletting the property to another party.

Based on the same reasoning, the breach of a prohibition clause on subletting will make the tenant liable to the landlord for damages, but may not render the sub-tenancy illegal.