Thanks all - yes, I did discover the info and various descriptions of tyre dimensions.
What became apparent when I attempted to measure my tyres is that the dimensions for tyre height are in an unloaded condition - i.e not really fitted and on the vehicle which would compress the tyre.
So when I measured mine it came out at about 68%. This means it could be 70 or 80% although I'm thinking 80% is more reasonable.
There's also suggestion that the 'C' after the tyre details indicates 'Light Commercial Vehicles'