Seen here with a mix of old and new accessories is an example of a modern UKSF Special Forces Support Group (SFSG) L119A1 with long upper.
Arguably, the most distinctive thing about it is the Ergo M4 Forward Rail.
Starting at the front of the weapon, there’s an old gen Surefire FA556SA can. These were certainly still in use with UKSF in 2017, if not later. 18 (UKSF) Signal Regiment L119A2s have also been seen with this legacy model of FA556SA.
A Surefire M600-series light with KM2 head provides visible and IR illumination. An LA5 mounted atop the aforementioned Ergo M4 Forward Rail provides visible and IR aiming lasers.
Note the tape switch underneath the Forward Rail, held on with a zip tie. Another zip tie is in use for cable routing.
The rifle’s receiver exhibits a Lancer Magwell – a look which has become synonymous with SFSG rifles. The Lancer item is a useful mag funnel, which can also double as a solid magwell grip.
A Magpul Trigger Guard (either MOE or Enhanced type – though if I were to put money on it I’d say MOE) is also present and again is thought to be part of the upgrade package associated with the modern SFSG L119A1; like the Magpul MIAD Grip and Magpul ASAP rear sling plate – also installed.
Keeping it retro (like the Ergo M4 Forward Rail and old gen suppressor) a Magpul BAD Lever is in use.
Note that an ambi fire selector assembly is present. A standard Trijicon ACOG and RMR combo is attached, in terms of optics.
To the rear, we see a Magpul CTR stock as opposed to the Magpul MOE which is often seen on SFSG L119A1s.
How current this build is I really can’t say, since it’s more than strongly rumoured that the L119A2 is rolling out across SFSG.