WP Jones was a successful gunmaker, principally to the Trade, although there are plenty of guns around with his name on them.
I am afraid that the concept of 'Grade' doesn't really work in the UK trade, only the real big manufacturers like Greener really had specific grades of finish or specification.
Your only hope would be to locate a WP Jones catalogue from the appropriate era, I have never seen one but I dare say they exist. That might give you an idea of where your gun lies in their range of the time.
Jones guns are usually of better than average finish for the Birmingham trade and I would place this on in the middle of the range. I restored one some years back which was quite extraordinarily highly finished and I suspect was a publicity piece for touting round the trade.
Here is a link:
http://www.heritageguns.co.uk/Jones%20BLE/Jones%20BLE%20Details.htm
