Update: Radar is still in hospital. I went to see him and we had a nice cuddle, he was very pleased to see me. As usual, the vets and nurses are all really taken with him because of how gentle and affectionate he is, so I think he's getting cuddles when I'm not there too.
They will keep him in until his hydration levels are normal, and to make sure he's getting on ok with the feeding tube (he seems fine with it, not at all bothered as far as I can see). He still isn't eating of his own accord. He seems to have a bit of a virus and is quite congested, they took an xray of his chest to check for fluid in the lungs and that seems ok but they did suction a load of mucus out of his trachea while he was under GA to have the feeding tube inserted. Hopefully once that clears up and the stitches in his throat are out he will want to try some food on his own.