Hi, I can help you with your question today.
I would first like to make sure that the scope of this service is clear. I am a veterinarian in the US, and I am able to give advice regarding his case.
I cannot examine Jag, and unfortunately cannot prescribe anything for him.
However, I think I can help him!
It sounds like your vet did a good job using the skin scrapings to diagnose his condition.
Treatment for demodex, however, requires DAILY ORAL administration of ivermectin.
We can also use a benzoyl peroxide shampoo to help.
The shampoo has "follicular flushing" activity, which can help to expel the mites from the hair follicles where they live.
In the US, you can purchase ivermectin at stores that carry feed and deworming products for cattle and livestock.
I believe the same would be true in the UK.
When you see my response, post back with Jag's weight and I can help you with a protocol.
We start with a lower dose of ivermectin and increase it over about a week.
I am going to give you a different volume to use each day for the first six days, building up slowly.
Day 1: 0.3ml
Day 2: 0.6ml
Day 3: 0.9ml
Day 4: 1.2ml
Day 5: 1.5ml
Day 6 (and every day thereafter): 1.7ml