Re Replies #'s 4 & 5. Luckily when I was back in the UK in June I was able to bring enough back with me to keep my gurlies pest free for a while yet. It's weird in some respects, my eldest dog whom we rescued as a very small pup rarely suffers from parasite infestations. She suffered with a form of eczema when she was little which took a long time to clear up and I often wonder whether she built up some sort of immunity to these pests.
Thank you all anyway for your helpful suggestions.