When the cause is a localised defect
If checks after heavy rain identify a limited defect and the surrounding roof and deck remain sound, a reinforced local repair may be appropriate.
The SealForge Kit contains polyurethane liquid repair material, separate fleece reinforcement, primer, catalyst and application tools for an appropriate local repair. It is £129.99 plus delivery.
If the entry point is still uncertain, the damage is widespread, the deck is soft or sagging, or access is unsafe, use a competent roofing professional rather than assuming a local repair is suitable.