sablebrush52 gives some great advice.
The early BBB's are highly collectible,
like these:
Antique BBB "Handy" Cavalier Pipe in CustomCase Silver Army Mount Straight Grain
&
Vintage BBB Own Make 6117 Cutty Pipe Unsmoked 1920s Bruyere Finish Featherweight
Neill Archer Roan has a great post about a duo of his BBB's,
http://www.apassionforpipes.com/neills-blog/2010/11/23/two-great-war-vintage-pipes-from-bbb-britains-best-briars.html
The writer Jacques Cole has a historical piece, although it covers most of the same ground as the Pipedia entry, it's still worth reading...
http://legacy.library.ucsf.edu/action/document/page?tid=xhj30g00
Several months ago I began collecting the old Britbriar, with a focus on blasted billiards and variants thereof and I have so far gotten myself a trio of Thorneycrofts. Each one has a different nomenclature style, one like yours, one with the big E made in but with the shape number stamped on the stem, and one with the more generic London.England. stamp...
...from what I understand, the Thorneycroft line came out in the mid 50's or thereabouts, I wish I knew the chronology of the stampings, but I'd guess the big E ones are the earliest?
I've been enjoying mine greatly, but I will offer some critique based on the several pipes I've experienced...
- the handcarved rustication on the shank isn't the best, at worst it can look sloppy, I've seen photos of some pipes that are poorly matched as far as "grain matching" goes and it spoils the aesthetic balance of an otherwise fine-looking pipe.
- the blasts moreso tend to be mediocre and shallow, at least on many of the examples I've seen in photographs, very rarely will you see one with an excellent blast quality, like this one:
http://www.smokingpipes.com/pipes/new/peterson/moreinfo.cfm?product_id=52449
I have a 636 with a rather gnarly blast, not to everyones tastes, but I find such examples to be interesting, visually I would like it much more if the shank rustication had been better executed, at places it's nearly smooth on the shank, also the box I have is the wrong color, it should be orange, the Thorneycroft came in an orange box...
- all 3 of the pipes I own have somewhat thin bowl thickness.
- the brass BBB diamond inlay is off-center more often than not.
- the bit is slightly chunky.
They are good pipes though and mine have served me well. I'm still looking for a few more to add to the stable, especially a 667, nice examples of the Thorneycroft line pop up infrequently compared to other marques, at least since I've been looking these last several months.
Congrats on your example, it looks fine indeed, although I dunno why they chose to stamp the top of the shank which sort of looks odd, but you got a sock too and that's very cool!