Thank you, MamaBas. I don’t want to move him from the special diet entirely without consulting the vet, although I have stopped using the Royal Canin dietary wet food and added a little Butchers Tripe.
At present he is fed breakfast and dinner of 50g RC diet kibble with 30g wet, plus 20-30g raw carrot for the crunch but usually now cut small for “tempting sprinkles”. At dinner he also has a small teaspoonful of natural goats yogurt (this was started a few years ago after reading your recommendation of it

, and it stopped the “little and often” morning poos of increasing runniness).
He also has lunch and supper of 25g RC diet kibble, plus one small dog biscuit when he is in his bed for the night.
If he doesn’t eat his meal, I take it up and re-present it at the next mealtime.