HI I will try and help
Did the the tenants notify you of the leak?
No, the tenants of the flats below notified the company that manages the building and they in turn notified me
Under s11 the landlord and tenant act 1985 you are obliged to repair and maintain the flat, sanitary items etc. Just because the rent isn't being paid doesn't detract from this obligation.
However if the rent isn't being paid and the property is in a state of disrepair you probably need to start eviction procedures
This can be undertaken by serving a section 21 notice giving them 2 months to leave, or by serving a section 8 notice where they would have to pay the rent within 2 weeks or you can bring action. have you served such notices on tenants in the past?