In the event of a tenant complaint or an incident the defence of "due diligence" may be accepted where it can be shown that the landlord or agent took all reasonable steps to avoid committing an offence - you will need documentary evidence of this.

A private owner letting a single dwelling (not in the course of business) may have a defence, whereas an agent acting on his behalf will not. However, an agent merely introducing a tenant and not becoming involved in the inventory or management of the tenancy my well be exempt from liability.