Bad news and yet hopefully good news!!
Woke up this morning to find Merlin still completely unable to put any weight on his left rear leg - but this morning his foot was swollen, warm to the touch, and obviously painful. Back to the vets we went... They suspected some damage or an infection in his paw, and sedated him to have a good look around. They found his paw was indeed infected, with an incipient abscess forming, so they opened it to drain. They looked, but couldn't find any seed or piece of shell or similar that could have caused the infection, but there was a tiny hole between his pads, as M.F. had suggested. So now he is back with us, dopey once again from the sedatives, and has antibiotics. They haven't bound the paw, but left it open to drain and heal in the air. Poor lad,hopefully this will get better soon - and phew!!!! if it really wasn't somehow down to his bad hips.
Here's the sad one, note the swollen back left paw.
I have to say though, that I am still very concerned about him. There have been several unexplained limping episodes, and I (and OH, who is normally much more stoical than I am) are still inclined to see an orthopedic specialist when we get back, at the very least to put our minds at rest, but also to find out if there is anything else going on.