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Thank you all for your advice.
I am going to up his intake to three sachets a day. Morning, dinnertime and night, plus his crunchies and ignore his asking for more, and that will be that for the time being. I rescued him from absolute filth, he was locked in a back room where you could hardly get in for cat faeces, poor little soul. My vet gave him a good examination and apart from ear mites he was found to be healthy, so perhaps he was always hungry and now he has a right softie in tow he is making up for lost meals!!!!