The "L" in the serial number is a big giveaway. Also, being that it's a No.4 Mk.1/3 indicates that it was a Mk.I* to start, which would limit the choices toeither Long Branch or Savage.
Nice rifle!
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But the "England" on the LH side of the buttsocket might qualify. Just pre-1968 import. (Some call the "England" an export mark, but that view is less in favor.)