Nice looking rifle. And how nice that it has load data engraved on the barrels (from your additional pictures, not the first).
London proofs before nitro. I'll wait for someone smarter than me to add a more useful reply.
Overall I like the condition. Lock to metal fit is still good. Doesn't looked messed with. The flat wide top rib and carving of the fences are earlier styles. You might narrow down the date by seeing when the Anson push button forearm release was patented, as it looks to have one in the last photo. Barrel is marked for use with solid, not coiled case, so that might give you another reference date if you don't find more on when the maker was active. Also looks to have rebounding hammers.
If I were wagering a beer, I'd guess 1874-1882, but I can't tell you that from the proofs, just that it's pre-nitro and post 1600s. You know it's post 1867 as that's when the maker moved to 25 Shude Hill.
Lastly, for some reason the marks closest to the barrel flats suggest the rifle spent some time in India or points further east.
Please keep us posted if you learn more.
