As per the previous post, I asked the farrier to have a really good look at Merlin's foot yesterday afternoon and after a lot of prodding he found a tiny compression towards the heel. I did ask if this was farrier-speak for "You're not picking his feet out properly" but he told me not to feel too bad about it, it was so small that if he hadn't been looking out for it and using a knife to clean the foot he might well have missed it himself. He cut it out - even cut out the hole is smaller than a 5p - and said that although it wasn't big enough to have caused the initial lameness it certainly would have accounted for his reluctance to put his heel down first.
It's been caught before the hoof started to crack and before any infection got in - he said that untreated it would almost certainly have gone septic - which is good news. Merlin was very careful about walking back down the field after his trim and I saw him standing in that mountain-goat-on-a-rock position when I checked on him last thing, but he walked out more comfortably and this morning he was only slightly unlevel and happily trotted up to the gate when he saw me :o)
So, fingers crossed, we've found the source of the problem and a couple more days of rest and relaxation will see him right. If this fog clears I'm going to give him a bath this afternoon - the newly shorn sheep are sleeping in his field shelter most nights, so when he goes in there and kicks them out he ends up lying in their mess and he has an enormous stable stain which three days of brushing hasn't got out.
His weight is between the 490kg and 498kg marks on the weight tape, so that's 6kg-ish on in 2 weeks. He's on one of my tiny handfuls of beet, soaked, with a scoop of garlic in the morning and nothing else but grass. I think I'm going to have to man up and start riding him in the school again once he's sound, just to help him stay under the 500kg mark.