Well, we need some more information, Joe. What variety are they? What situation are they in, such as a poly tunnel, conservatory, sheltered, sunny courtyard, etc.? What kind of watering have they been getting? What kind of feeding have they been getting? Any signs of pests or diseases? Are the stems breaking, or is the fruit peeling off the stem? Is the fruit changing before it falls--i.e., rotten spots, mottling, withering, etc.? All of this will help us to help you.

the most likely cause is lack/insufficient water. as the fruit swell they need lots of water.