Thanks henwife and hen-gen.
The hens have not been eating eggs laid in the nest box as the birds are laying them anywhere but the nest box!
They sit in the box for 20 minutes then walk out and lay them in the middle of nowhere.
The coop is new and red mite clear. The boxes are dark and comfy.
Fortunately the shells are getting firmer so I managed to retrieve the eggs today before they were eaten.
I have fake eggs in the nest boxes.
There's two out of the six 23 week old birds laying and both have chosen to lay outside the coop, all advice is appreciated but I can't imagine any way of getting them to lay in the nest boxes if they don't want to!