The P226 (classic/non-rail) is the L105A1. Not the UOR pistol. In service for a very long time.
The P226R is the UOR - L105A2. Also had an improved corrosion resistant finish.
P228 was the L107A1. Never part of the UOR. As with the L105A1, it's been in service for quite some time.
P229 is the L117A1. Some were purchased as UOR (dog handlers), some were not. The Royal Military Police and RM Fleet Protection Group bought their own.
You can probably guess why some of these have official designations but were not issued in the UOR.
L6- has never been used for a pistol. Similarly L106- hasn't been used.
I suggest it'll be the L131A1. Last piece of new kit was the L129A1, and there's already an L130 in service. However, this of course goes by the belief that the MoD give things designations in a logical way...
Also - whilst the photo of the prototype on TFB is the one I meant - it seems that the issued Glock doesn't have an extra safety afterall. Looks like the media got it wrong (looking at the Guardian article, which was the first to report this on Wednesday, they've removed all references to safety...

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