Thanks guys for your replies!
Caro: I think it was more the chicken bone though - for some time after his licking stopped in January I was still feeding him raw chicken and minced pork/beef but with salmon bones instead, and he was fine. It was only after I realized the amount of fat in the minced pork/beef supplied had increased (and the respective brands introduced 'leaner versions' at twice the cost) that I decided to cook his meats and remove the amount of fat I fed. But yeah, I've definitely considered if he just doesn't cope so well on raw. I couldn't quite believe or accept that for some time though, given that I'd switched him to raw believing it was better for him.
I've indeed tried to keep Chiral's recent meals as simple as possible: eggs and pumpkin, eggs and potato, most recently just egg whites in water (all cooked). As of yesterday, he was still licking his bum. I must say, though, that each time I changed an ingredient he'd actually stop licking for at least half a day (after that meal, till the next feeding) - only to start again. Out of desperation I fed him his original herring kibble last night, waking to no bum-licking. I'm just waiting to see when that would reappear though.
I'd actually tried to buy beef rump steaks, but Chiral's a gulper, and so I had to hold on to one edge of the steak to force him to chew. He tends to use his incisors, and I noticed after a few days of such feeding there seems to be a hairline crack/tear on them. It didn't seem to bother him, but it freaked me out enough to stop doing so. I realized that when he crushes pork soup bones it does do a good job cleaning his back teeth, but I think pork also gives him itchy-bum.
I'd last given him Frontline Plus in July - but I've also heard a lot of reviews about Frontline not quite working for a lot of people too. Sharon brought that up too. Hmm. I'd bought the 6 pack!
Sharon: I'm hoping it's not the food too, but for it to coincide with my reintroduction of raw chicken bones seems to be more than a coincidence. He's generally still got a good appetite, eager to go on walks, responsive (though I have definitely noticed that he seems to put his head on the floor a lot quicker after lying down, compared to previously), scratches occasionally or especially after I give him a full body rub - so it isn't as though he's scratching incessantly, but it is still a problem, and I do not want it to escalate to any GI issues or anything.
50/50 white vinegar to water seems to provide some itch relief, and I'm hoping the vinegar also acts as an antiseptic somewhat due to its acidity. Otherwise I do have some steroid cream that the vet had previously prescribed for his pressure sores.
I'll update again how he's doing on back on kibble. Not my first choice (although my folks have been resistant to the whole raw thing and believe in kibble), but if that agrees with him most I'll just have to accept it. I'm expecting the butt-licking to return though...