Although it's not my specific expertise, I checked in my copy of "Without Warning" By Clive Law. The mount doesn't look at all the same in the book as what's pictured, although it is a Lyman Alaskan scope, as one can see from reading the inscription on it. The pic shows the screws holding the mount on the receiver as being at a 45 degree angle, whereas the pics of this one show them level (horizontal) to the axis of the rifle.
According to Clive's book in reference to the Lyman Alaskan scopes, it has been established that 350 of these were purchased and provided with mounts manufactured by Small Arms Limited..
I think wheaty and some other really smart Enfield collectors will be able to clarify this when they log in.
Edit: BTW, here's an interesting Quartermaster Stores ad in the "For Sale or Auction Elsewhere" section for a WWII Enfield No. 4 MKI Manufactured in Canada with Lyman Scope
Regards,
Badger