Thank you for your swift response. I have looked at Charcot-Marie Tooth disease and the stmptoms described match mine so closely that I am going to contact my neurologist (who deals with the mytonia) to see about being tested for it.
It seems strange that after going nearly 40 years without a "formal" diagnosis I should have come one step closer through spending 5 minutes on the internet; especially as I have been examined by British doctors for most of my life!
Check out Charcot-Marie Tooth disease. Sounds odd to think of the foot being related to something with "tooth" in the name, but this is a progressive neural atrophy of the muscles supplied by the peroneal nerves that can affect the muscles of the foot where one set of muscles are stronger than the other causing a club foot look. Clawed toes is a side effect of this disease. Nerves are not affected and it is diagnosed by an orthopedist, not a "foot" doctor.