Thanks again. Was just discussing this with my housemate and she was suggesting the same - about more painkillers / anti-inflammatories. Will phone vets on Monday and ask if they will prescribe some oral metacam for him for a while.
He struggled a bit on the Litter Kwitter earlier and didn't pee which worried me, but I opened the normal litter tray and he did go in that. He had used the LK in that last few days though.