Thanks so much for everyone's thoughts and kindness.
We have had the first lot of x rays back and been recommended to see a neurologist as there are certain images they couldn't get as the spine is so well protected behind bone etc.
Rufus seems happy and well, but he finds it very hard still to use his back legs when getting out his basket. When he drinks from his water bowl, his back legs slide flat under him rather than keep him up. It is very clear they are not doing what they should be doing, regardless of age and growing bones, so I think seeing a specialist is the only answer at this point. We've eliminated a number of parasites through doing blood tests, but given his reflexes are so bad in his hind legs, it is more likely to be central nervpus system. He really only uses his back legs when he is on the go-sounds odd but most the time he flops down on them and uses his front ones.
It is very worrying but trying to keep positive that it will be something we can fix, rather than something debilitating.
Anna x