Illustrative example
Water has come through the same bedroom ceiling three winters running from a flat roof over the neighbouring flat. Each spring the landlord repaints the ceiling and pays a small sum for the inconvenience. The tenant wants the roof fixed, not another payment.
Section 17 lets the court order specific performance of a repairing covenant, and it removes the two objections that used to defeat such an application: the order may be made whether or not the breach relates to a part of the premises let to the tenant, and notwithstanding equitable rules about mutuality. The fact it turns on is that the defect is in the roof over another flat, which is exactly what the first of those makes reachable - though the remedy remains discretionary and the works have to be capable of being specified precisely enough to be ordered.
The landlord commissions a roofing survey within a month and carries out the recommended works before the following autumn, with a payment schedule agreed in writing and the tenant giving access as needed.