Not a Brown Argus, but a female Common Blue

I was enjoying the sunshine in the garden this afternoon when I noticed a small butterfly flittering about.  It eventually came to a rest on the osteospermum and gave me enough time to race inside and get the camera.  A careful examination of the underwing confirmed that it wasn't the brown argus I'd hoped for but a female common blue. I wasn't initially sure as it is easy to confuse the brown argus with a common blue female.  It kindly stayed still for more than enough time to take plenty of shots and select the background of my choice in the process.