This is most odd because raw food is reputedly good for coat and skin. I am tempted to think that as they are both experiencing problems it could be due to an external factor, not food.
I note that you live in Wales. I have a friend who lives there too, not far from the coast. Her little dog has this problem every year in the summer/early autumn. It is due to mites that she picks up on walks, particularly on the dunes. Not sure, but I think they are called harvest mites.
I have another friend who lives in West Sussex and her dogs have the same issues at the same time of year. She tells me that the area is quite chalky.
Anyway, both struggle with treatment for this seasonal itching. Wales friend currently uses Malaseb regularly and takes the dog to the vet for antibiotics because the scratching causes bacterial infection which makes the dog itch/scratch more. She also puts a collar on as necessary to stop the dog scratching. Think she also tried Leucillin spray but can’t remember if it worked. Before changing food it might be best to have a skin scraping done by the vet and to start a course of treatment.
On the subject of Canagan, they seem to be a good range of foods with mid range protein levels. I gave it to my dogs once or twice but it was a long time ago. They were ok with it but it was not suitable because they are dogs who put weight on easily and they gained quite quickly, despite giving much below the RDA. Not the fault of the food - fat and protein simply too high for my dogs.