Thank you for your comments - very much appreciated. I certainly shall try the chicken broth, one of his favourite flavours. I was not sure if this would add to the kidney damage. He already has had two teeth removed since I adopted him three years ago but, when he had a blood test two months ago as part of his yearly checkup, the kidney condition was mentioned. A few weeks later I had him back as I was aware of a recurrence of his tooth/gum problem - to be told that it was a chance to take if he was anesthetised, hence the introduction to the renal food which I am told is forever. He was also prescribed Tramadol to alleviate the pain, which I administer morning and night. I always made a point of giving him a variety of dog food, and cooked chicken as a treat. I'm not surprised he is not finding the boring food to his taste.
Thanks again for your advice and I hope it does the trick.