First, a tomato won't produce fruit if it's under stress. Is it too hot, above 90F? After checking for sufficient, sun light, water, air circulation, try hand pollination with a small brush. Maybe the bees aren't up to the task.

Hi, try giving the canes supporting the plants , a gentle tap every day, to help pollination, or do as Bathgate says, Derek.

Won't be too high temps. Bathgate... I'd suspect lack of sun light but you've covered other possibles as well...

Firstly tomatoes aren't normally pollinated by insects. As was suggested you need to shake the flowers or tap the flower stems daily which help transfer the pollen from the anther to stigma. Also spraying the flowers can help as pollen setting is best under humidity. White blotches on leaves could be mildew, but need photo to make it clearer.

Yep tap the plants to pollinate - fruit will or should set in sun or not - never known the sun to help pollinate plants - But maybe I'm missing something here ?

Lack of sun won't stop pollination Triffidk., at least I don't see why it should... can stop the fruits actually forming though if it is too cold.

The bees are all over my tomato plants and they are weighed down heavily with developing fruit. I've posted some pics in the main gallery. I've surrounded them with sunflowers and other plants to help draw them in.

IF you don't have bees - resort to the tap tap method or a small brush which is more precise.