Little courgettes going bad

Hi all, I wonder if anyone can give me some advice please?

I've got a courgette plant which has been developing little fruits, but when they get to about 3 inches long, the end starts to rot.  Does anyone know why might this be, and what I can do about it? My other courgette plants aren't at the fruit stage yet

The plant came from a garden centre, hardened off, and planted out at the end of May in a bed which had been dug over and had compost added.

Thanks for your help

Sal

With all the wet weather i find the flowers have been getting wet and staying wet this has caused a few of mine to rot from the flower end, i've started to take the flower off as soon as it shrivel's and this seems to help.