I think the guy doing the numbering for the "R" pre-fixed No5's must have had several off days. Mine is clearly marked for 9/44, serial number R1106. I've examined this rifle in minute detail and it's definately a pukka No5 Mk1.
http://i269.photobucket.com/albums/j...y/SS100197.jpg
Don't worry about the "wobbly" nature of the writing, that's just me being a bit rubbish tracing it over with the Dremmel.