Ok, I think I have resolved this. It could have just been some images linked to http not updating to https. It applied to ANY images added via the TinyMice box, all other images in CS were updated to https.
Use www.whatnopadlock.com to see where a problem may be. It is most important in CS as even if you use a gateway, the CS site will keep warning the client it is not secure, so may send / scare sales away. And to fix it you need to set the whole site as https in Generals tab.