Was there a placard for this display? Two unusual guns there, the bottom "sten" being very unusual. The top is just a mkii with a pistol grip and it's trigger guard cut off. The bottom however, at first glance appears to be a mkiii, but it has many differences. It has a bolt-hold-open/safety, a smaller magazine and magwell, a different trigger, and finally, a smaller diameter receiver tube. It is very unusual. Perhaps a prototype mkiii designed to use different mags, or a training gun?
I'm not sure either - and I can't remember if there was any info nearby about them I did notice at the time they looked a bit different, but I didn't/don't know that much about Sten variants.
I might just be imagining this, but part of me remembers (or my scattered brain has made it up) that the trigger guard folded to one side, and is just out of sight in this picture. Again though, that's probably wrong.
The M-79 grenade launcher has a trigger guard that does that, but I dont see any point where this one could.
I found out the sten on the bottom is not a sten though. It's a model gun that shoots blank ammunition. Pretty weird it ended up in a museum, and even weirder it has a added safety feature, though it does not shoot. For more info on that one, google modelguns.co.uk/stenmkiii