So, we left Copper to it and I calculated that yesterday might be D-Day.
I've been away a few days and decided that I should freshen up the coop as OH will feed and water when I'm not here but not muck out. Mindful that Copper needed to be as undisturbed as possible I gently got rid of soiled bedding from under the perches and put new fresh bedding in place. Copper was just watching me, but was also making quite a few chuckle noises - which is not normal for her, previously she had just fixed me with her beady eye.
Anyhoo I then heard cheeping

and was rewarded with the sight of a light coloured chick milling around by Mum's chest

I withdrew and called to OH and he came up from the barn to have a look
Then Copper started making more determined noises and another chick - very newly hatched I think - appeared as well
I left them in peace for a few hours then returned for a few piccies
Ridiculously proud

First born livestock on our smallholding (not counting the bees!)