Thanks for sharing pics of your rifle. Congrats on getting this interesting, classic rifle. It is really quite wonderful—though it needs some restoration.
Here’s what I can see from your photos. It is not a commercial rifle at all—it is a government rifle through and through, with one exception: the bolt head (not necessarily the entire bolt) has a commercial patent stamped on it (Patent 19145/90), which means the bolt head was from a commercial rifle. First thing to check is if there is a number on the bolt handle and if it matches any other number on the rifle. If it does not match, then you have a commercial bolt (from a “Lee-Speed”) that is mismatched. If it matches, then for some unknown reason, the manufacturer (LSA Co.) used a commercial bolt. We know the rest of the rifle is not commercial because there are no commercial proof marks on it—only Gov’t proofs. For information on what the 19145/90 patent means, see the article here:
https://www.milsurps.com/showthread.php?t=76034
So what do you have? It is a CLLE Mk I* (pronounced “Mark One Star”). CLLE stands for “Charger Loading Lee-Enfield.” These rifles were conversions of the Lee-Enfield Mk I* (beginning in 1907), to convert them to charger loading (i.e., to enable them to be loaded with stripper clips, or “chargers” in
British parlance). So, your rifle was originally a “Magazine, Lee-Enfield Rifle Mk I*” made by LSA (London Small Arms Co., Ltd, located in Old Ford, Bow, London) in 1902. That is what the right-side markings on the butt socket tell you. You are correct that “ER” stands for Edward Rex (he had just become king after Queen Victoria died in 1901). This rifle was always a Lee-Enfield (with Enfield 5-grroove rifling in the barrel)—it was never a Lee-Metford.
The conversion details are indicated on the left side of the butt socket: converted by LSA to CLLE Mk I* in 1909. For details on this conversion (exactly what was changed) see your
Skennerton book. He covers all this, so I need not repeat all that here. Basically, the charger bridge was added, the sights were upgraded, and the front sight got a pair of protective “ears” and the bolt cover was removed (it doesn’t fit anymore when you add the charger bridge). The barrel is stamped ’11, so this rifle probably got a new barrel in 1911, to accommodate the new MkVII ammunition, and at that time the front volley dial-sight would have been changed to a plate marked “CL” and graduated from 1700-2700 yards (you can use one from an SMLE, but it won’t be correct).
Keep in mind that all these changes were legitimate Government-authorized conversions… not someone monkeyng around. They were official upgrades for use by the British military, and they were definitely used. It is almost certain this particular rifle was used in World War One. Such changes do not make it less valuable or less desirable.
For details on how this rifle started life, see Skennerton page 450 (Magazine, Lee-Enfield Rifle Mk I*)
For details on the conversion it underwent in 1909, see Skennerton page 457 (Charger Loading Lee-Enfield Mk I*)
Anther great book from Skennerton (inexpensive) that is extremely useful for collecting or for restorations is “Lee-Enfield Parts Catalogue”—No.23 in the Small Arms Identification Series (S.A.I.S.) It illustrates the changes in every part from the first Lee-Metford all the way to the No.4 rifle of WWII. You can find it here:
http://www.skennerton.com/sais.html. That little book is money well spent.
As for the markings on the butt plate (HQ/ASC/SMD), I’m not an expert on those, but you can look them up in the Skennerton book, or in his other book “The Broad Arrow.” Or ask on the forum—someone will know. I am not an expert on all those unit markings. My area of expertise is the commercial rifles (Lee-Speeds).
You observed that it has a "B.E. crown and date”— do you mean the stamp on the left side of the action, where it meets the barrel? Looks to me like it is actually Crown over X (rubbed out or lightly struck) over 88. The letter x (as you can see in other inspection marks nearby) is the factory code for LSA. These are all Government marks. I do not see any commercial markings on this gun, except for the bolt head.
As for the restoration, I am not an expert on that sort of thing—I’m mainly a historian and researcher. I have examined a large number of Enfields, especially the commercial models, but I’m not the best guy to advise you on where to find the missing parts that you need for the restoration. I think the first step is to determine exactly what you need (now that you know it’s a CLLE MkI* it should be easier) and ask on the forums. Someone will have it or be able to help. Be patient—the part you need will turn up eventually. I can tell that you will need the correct volley sight and the rear sight slide. As for the bolt, it is the correct pattern (despite having a commercial bolt head) so I would just leave that as it is. Still, I would like to know more about that bolt. Please let me know what other markings are present on the bolt handle and the cocking piece. If it is a mismatch, and you want a Government bolt, then it won’t be hard to find one (with Government markings, maybe even an LSA one), and you can sell me the commercial bolt—I’ll find a use for it on a Lee-Speed. However, we do not know yet whether the bolt is incorrect—it is unusual, but not necessarily incorrect. Maybe LSA just used a bolt that they had in the bin, and "commercial vs Govt" didn’t matter for some reason. The commercial bolt head (although incorrect for a Gov't rifle) is actually more scarce and desirable by people who are restoring Lee-Speeds, so you kind of lucked out on getting that.
Good luck with this restoration—an admirable project. This fine rifle deserves a proper restoration and display. The guns of the London Small Arms Co. have been a special interest of mine.