Cloudy Summer....

Light rays come through clouds regardless, so don't worry. You might not get as big a yield as in a sunny year, but you will get cropping. As for them stalling now, it's more likely the cooler weather since all squashes prefer hot weather. 

Although it is warm in the day we are still getting some chilly weather at night. That said it will not go below 17 degree's tonight. A lot of squashe's and bean's have yellow leave's on my site.

Anythings go to be an improvement on last year just less rain is good I had only 2 courgettes a week from 4 plants last year.

What would you normally expect from 4 plants Madame?

Fair enough

In a good year with four plants you would be feeding your family and your neighbours as well. They are very prolific given the right conditions - unfortunately last year was not a good one. My plants all upped and died on me. So far this year they are doing better. 

I know many people on this board had no success with courgette in 2012, but because I had mine in a grow back because of the lack of room, I managed around 15 6 inch fruit off 1 plant     They really seem to benefit from the increased warmth you don't get direct in the ground (unless your using a raised bed). I found that as long as they had plenty of feeding and water, they don't actually need that much direct sun and perform better than many of the tender crops in a cool summer