The absence of the crown indicates that the rifle was proved ("proofed") prior to 18 Oct 1898 and given only the standard proof. I am not aware of any Liege proof mark specifically for guns shipped to England, but at one time (1893) the Germans would allow importation of Belgian guns only if the oval had a crown, which indicated a higher level of proof. The Belgians complied for guns destined for Germany and then extended the higher proof level (oval and crown) across the board (1898).
Louis Nicholas Auguste Flobert of Paris was the inventor in 1857 of a type of rimfire cartridge using only the primer explosion to propel the bullet, like the more modern BB Cap. The invention may have inspired Smith and Wesson to use much the same system, but with a powder charge, in their first revolvers. He also invented a system of rifles and pistols in which the hammer served as both the firing mechanism and the breechblock. The heavy hammer had a smooth face except for a protrusion which contacted the primer-filled rim and fired the cartridge.
The combination of the hammer mass and the momentum from its forward movement served to prevent the cartridge case from blowing backward. If a cartridge is used that is more powerful than Flobert's, the cartridge case will blow the hammer back and fly out of the chamber, possibly injuring the shooter.
Warnant, a Belgium, invented a breech block that could be used on Flobert type guns but which would allow use of a more powerful cartridge. That is the system used on the gun in question. The arms of the breechblock are screwed to the barrel and I have seen them with screws broken or so badly worn they will fall out if the rifle is turned over. Even though the Warnant system will allow the use of more powerful cartriges than the original Flobert system, it is still quite weak, and I strongly recommend against firing one.
Jim