Thanks for the wisdom, feline!
I'll pass up the offer of food as it would be fairly costly to post and we still have a fair amount of kitten food remaining.
ETA Scrutinising the Sainsbury's website for info about the various foods, it seems neither the energy, nor the carb content are stated. The 'moisture' ie WATER content is given for wet food but omitted for 'dry' food, which I'm sure is not totally water-free.
I think I saw energy content a few weeks ago, conveniently given as the percentage recommended for an ADULT HUMAN. They have appeared to remove this anomaly.
Making a halfway informed choice is difficult!