The "box" or "detachable" magazine may be a modern misdirection - at that time, was not many years since military British rifle had magazine cut-offs - was not as if riflemen on the line could be trusted to conserve ammo - so was normally fired single shot, unless specifically ordered to open up that cut-off. I think even WWII British, Australian and Canadian doctrine had soldiers using stripper clips to reload their Lee Enfield rifles - so far as I know, replenishment ammo showed up at the front lines in stripper clips (chargers) that fit and worked in both No. 1 and No. 4 Lee Enfield and the P14 (No. 3) - except, as noted above, the Lee Enfields held twice the number of rounds compared to P14. I do not think that the magazine was to be removed from the rifle, except for cleaning - as if the "detachable" part was not how we have come to think it can be used.
I do recall growing up with various Lee Enfield No. 4 sporters in the 1960's - most magazines had significantly mangled feed and guide lips from trying to use them as a "clip" - leads me to put some credence to the thought that the Lee Enfield magazines were designed to be used as "fixed magazines" - of course with the advent of scope sights, that entire "charger top loading" thing seemed to go away - so many people are left with the idea that their Lee Enfield "detachable magazine" works OK with a scoped Lee Enfield rifle - my Dad certainly thought so.
Some years ago, an acquaintance brought over an iron sighted SMLE (No. 1 Lee Enfield) to get "fixed up" - I completely dismantled it and found nothing broken, to "fix" - simply what might have been 100 years of grunge and crap in there, and some minor "tweaking" to the magazine guide lips. When cleaned and lubed, I re-assembled it - first time with some dummy rounds, I remember opening the bolt to see if one had actually been chambered - it was, by far, the slickest operating bolt action rifle that I had ever used - noticeably better than the Mausers and commercial rifles that I had before or since. And there is at least a dozen P14 and M1917 sporter rifles here to compare with. I have read that various "Krag" rifles - made in Norway or in USA - might be similarly "slick" to operate, but I have never handled a Krag to know that.