Well, day 4 update, for the record, as promised.
Amazon order arrived Sunday, so into the shower with a none too enthusiastic Jack. Aromesse recommend spot testing first, but didn't find that out till afterwards. Had no problems. Used the Dermacton shampoo as per instructions (the bit about spot testing is at the bottom, so missed it...) Comes in a hard, not unpleasant smelling bar. Jack moaned like mad, shower hose a bit too short, and I ended up almost doing my back in - but it works!
Gone from scratching every 10-20 mins to (almost) zero. So far so good. Having a good scratch behind the ear now and again doesn't count. Have the spray on standby, but (so far) haven't needed it.
For info, shampoo bar contains no soap. Lathers up quickly and should be left on for around 5 mins. Still looks unused and although not cheap, I've no doubt it will last years. It does have a strong 'clean' smell that even the original wrappng and a couple of plastic food bags doesn't mask.
Fingers crossed, job jobbed. Am now a convert to Dermacton/Aromesse. It's a pleasant change when products work rather than wasting money. Just hoping his feathering grows back quickly (he has/had lovely feathering on his tum that he's self-stripped with scratching). Will use up the Yumega Itchy Dog, but this takes a while to 'kick in' anyway. Difficult to tell at this stage if it's helping. Given the price, I'm hoping so. After that I'll try Archie bean's suggestion of the non-stinky stuff.
**Bonus - it's also cleared up some dry skin on my hands!
Many thanks again to both Pam and Archie bean for the suggestions. You both rock!
Linky (Aromesse are cheaper than Amazon):
https://www.aromesse.com/skin-problem/Dermacton_Shampoo_Bar.html