Yes, these are rifle bags for Lee Enfield rifles. There were two lengths produced, 44 1/2" long for the No. 5 and 47" long for the No. 4. with the pocket designed to hold one 50 round bandoleer. These bags were used by troops who were rotated off the Front Line but were still close enough to be subjected to mortar or artillery fire, hence the need to keep dirt and moisture out of the actions. There were larger white canvas bags with slings used during periods of heavy snow. You can see pics and more detailed description of these rifle bags on p. 78 of David Gordon's revised and expanded Weapons of the WWII Tommy.
CHIMO!