Welcome from the UK. No doubt you will eventually read about Diatomaeceous earth (sp?) (DE) which is a chalk dust you can buy and feed to your chickens and dust them with it. Its razor sharp at cellular level and cleans the mites/lice/worms up by slicing their skins and they lose their inner fluids and die. Read up on it and use it regularly - it doesn't harm the chickens at all. Also, putting apple cider vinegar in their water (1 tbsp/gallon and use plastic dispensers, not metal) gives them some protection from pests and helps keep their systems in good shape.
I did try the DE. I am not quite sure how you do the dusting process though. I just sprinkled it on the birds. Not sure if that is actually how you do it, but any proper instruction on dusting the birds will help. Only the turken seems to have the mites/lice (ir what ever they are). The eggs look just like the pictures someone posted in a previous post. And the eggs that hatched have little brown bugs that are about a millimeter.