[Nube]

Thanks all. I have removed the carpet from the living room on which he often caught his nails which did not help with the limp leg. He had a long and energetic run around yesterday, and has been climbing onto the cushion I was sitting on and begging for food, so I do not think he is in any particular pain. His lower limbs are definitely weak, a couple of times he rolled onto his back and had difficulty getting upright, and sometimes he dragged the right one behind.
I have also bought a stone slab today, will wash and sterilise in the oven and put next to his water bottle to ensure his nails get shorter. They are not very long but I do not risk cutting them as with his damaged legs am very wary of potential accident.
I will consider removing the second level when cleaning the cage next (which we do very seldom these days to minimise disruption and stress - he is well toilet trained so I just do spot cleaning now and then). Am just worried he will be a very disappointed hamster if we do that...