Thanks Donna, his poo seems a little better today and I have some good news
Heard from vet and Dexter has tested negative for both TF and Giardia! Obviously I know there can be false negatives but with his poop now being firm everything is looking positive.
Muskey, our Burmese hasn't been tested yet and we are going to do that next.
Vet has asked me to keep Dexter on lamb for another week and she will give me another ring on Friday to see how it's going. She suggested we could at some point try him on a lamb based diet for cats who have itchy skin as they usually do well on that although she also said there is no reason we couldn't try him on normal cat food at some point although as you can imagine a bit reluctant to do so!
Won't be putting the two cats together again until we have results for Muskey and Dexter is on a diet that Muskey can eat too.
Can't tell you how happy I am feel like celebrating