My black and tan, Riley sees Dr. Podell, a neurologist at http://www.chicagoveterinaryemergency.com/ in Chicago for her SM. He has been absolutely wonderful to us. He diagnosed her within a minute of hearing her symptoms and looking at her walk and watching her behavior. She has seen him now for over 5 years. He has a cavalier and is very familiar with SM. He may be able to help you with Leo just with a diagnostic physical exam. If you can get a video of his air scratching that would be great. You could talk to him about wanting to wait for an MRI until you get back to the UK, but maybe ask him if he feels Leo might be helped by some medication. I have nothing but good things to say about him. He has done surgery on two of my dogs - one for SM and one for cervical disc decompression. Good luck.
I didn't know you lived in Chicago and I didn't know Dr. Podell did Riley's survey.