Headstamp tells the tale: Royal Laboratories made it (R L) and it is Government property (/!\).
As for the rest, what they tell you is what specification it is made to (Mark II) and what powder it is loaded with (Cordite).
This cartridge was manufactured from about 1894 until some time in the Boer War, more or less. At that time, the British were experimenting with a variety of 'improved' cartridges: the Mark III with a soft-point bullet and the Marks IV and V with hollow-points. Eventually, they standardised on the Mark V, just as the hullabaloo started and the world got together at The Hague in an effort to ban the terrible new British ammunition, which had become somewhat of a cause celebre among the prople who stayed in the cities and did not have to defend themselves against the guys with pointed sticks and long, long iron heads on the things. The world banned the British Mark III, IV and V ammunition.... but the British had, on adoption of the 'Dum-dum" bullets, put the old Cordite Mark II (your cartridge) out of production, declaring it obsolete.
So the British had to do something, so they brought the old Mark II back, calling it the Mark VI (there was no difference at all) and made it under the new name until 1910, when they brought out the pointed-bullet, somewhat impact-unstable Mark VII, which is still being made.
But a lot of cartridges like yours were shot off in the Boer War and in about fifty different rebellions and police actions and so forth around the world.
It isn't worth much.... couple of dollars, perhaps..... but it is a REAL historical artifact and it is more than 110 years old.
You know, something like this could be the starting-point for a really decent cartridge collection......
Just thinking.....
When Peter Labbett wrote the book on the .303 cartridge, he used his own collection (more than 1800 different cartridges) as the basis, then borrowed specimens from other collectors to make up the gaps. He once told me that there were 3600 different .303 cartridges, including all the really squirrely ones that most of us have never heard of.
Start with this old girl and you are on your way.
Have fun!