Could be sunburn, but if you've left them out overnight, the other cause of white patches is cold temperatures.

There have been some cold nights, I would put them in at night until the end of the month.
what seems to suit them is stable temperatures not high/low peaks and troughs

It could be caused by stress to the plant due to a sudden change in its environment, i.e. a drastic change in temperature, especially cold nights, a lot more sunlight suddenly getting to them or a sudden change in how much water they get.

The other thing that can cause this problem is if you get water on the leaves. The water droplets act like a magnifying glass that causes the leaves to burn, but this usually shows up as white spots.

I'm sure that once they get used to their new position they will overcome this stress. The damaged leaves will fall off and new laves will grow in their place. When they reach 5 - 6 feet tall and get to adulthood they will be fine and produce lovely fruits. :o)

Thank you all very much for your kind replies. I have decided to bring the plants in at night for the time being although they had only been out for two nights both of which were very mild. Hope I've caught them before it's too late.