Hi Susie,
My courgettes have always done better in the ground than in pots...In the ground, they don't seem to need anything but harvesting. In pots, the fruits often begin to form then fall off before they're ready.
Due to lack of space this year, I'm giving them another go...in really big pots with lots of feeding...they're really greedy! Still too early to say whether it'll work, though...

Bees seem to have trouble finding them in pots, too. You may have to hand pollinate them to get good courgettes.

Do you know there are male and female flowers? The female ones have tiny little swelling behind the flowers. Often the plants produce quite a lot of male flowers before the female ones get started, so this could be the reason.

Thanks everyone.