IMO, 55K GBP is high for this gun.
I would think in the $54K-$60K US if it were on the market. Still not chump change of course.

There are a couple ticks as mentioned previously which detract a little, such as the shortened stock and the pitting, but would have no effect on the guns performance. My suspicion, considering the barrels, is that they have been reblacked at the time the pitting was cleaned up. Could have been long ago when this was done. This isn't a big deal of course, but some high end collectors scoff at any refinishing.
The little ivory can is for spare parts - firing pins, screws, small springs etc. It is my impression that these little parts would normally be in the ivory can and spare sights would be held in the grip cap compartment. Of course, a hunter could also put a spare firing pin in the cap too when out after game since his guncase would very likely be back at camp. Sometimes you see the same little can made of rosewood or ebony.
Great thing about doubles is that if one lock has a broken spring, then you still have a perfectly serviceable single shot on the other side of the action!

All in all though, a terrific rifle! These will always command a premium on the double market, so your money is pretty safe in a good H&H Royal. BTW, IMO, it is a Royal eventhough it isn't engraved as such. (that is a sticking point for some folks too...)