It depends on what's causing the leak. If a tile has blown off the roof due to high winds, then you might well be covered. But if it's due to deterioration of the roof over time -ie wear and tear - then it probably won't. You really will have to look at your particular buildings policy.
If you know a builder who can "verify and prove" that the leak was caused by storm damage, the Insurers should pay out. You know what I am saying here, so I cant endorse this action, but it goes on all of the time. Ok, I admit to having done it. Still feel a bit guilty even now!