Okay, she's a nice old First World War rifle which was kept after the war and likely refurbed in the early 1920s. There were few new rifles built in the years right after the War but they rebuilt literally millions. The rebuilt rifles went partly into store, about 100,000 came to Canada and hundreds of thousands more, along with Rosses and P-14s, were given to NEW armies which previously had had nothing: Latvia, Lithuania, Estonia just for starts, and more to Greece and other Allied countries which had had a hard time during the War.
Where this one might have been, we don't know. Those GG inspectors' marks are ones I haven't seen before.
In the run-up to War 2, the British Government had this insane idea that if they destroyed all of THEIR guns, that nice Mister Hitler should reciprocate and trash all of HIS guns. So tens of thousands of Lee-Enfields were scrapped or turned into deactivated Drill Rifles. Yours escaped this particular bit of madness and was on-hand during the BLACKEST part of War Two, when the Brits had one fairly-modern rifle on hand for about every six men who NEEDED one..
Following War Two, the old girl was rebuilt again, this time in 1953.... and that is a bit odd in itself. I think this is one of the LATEST rebuilds of an SMLE which I have seen coming out of England. I not that it has had what appars to b a commrcially-markd BSA brrel fitted..... which makes sse, being that BSA, at that time, had the only plant capable of making barrel for an SMLE. Enfield supposedly stopped all work on SMLEs in 1943, although I do have an experimental which they fitted with a new barrel in 1945.... although it could have been old stock.
But your rifle was rebuilt to "New" in 1953..... and they don't come any better than that. Likely it would have been sold off as surplus very soon afterward.
This one MUST go to the range!
NICE toy!