Weapontech there are some builds on other forums, they are mostly US stuff which is closed bolt or hammer fired designs, but that should apply up here, what got me started is I saw an ad in the EE for the mk3 sten parts kit, which has the majority of parts you need for the build, need to make the tube and the magwell as these are the reciever, the modifications to the bolt and the trigger mechanism seem to be easy, just takes time to do it right.
I have to say stencollectors thread here is one of the nicest ones, there is also one on milsurps by claven2 and navyshooter has another great thread on here. They used the closed bolt sas-3 or OI kit design, which is a much better one then open bolt, but having said that the kits for sas-3 style closde bolts have mostly dried up.
You could build the closed bolt kit but ######## got approval for an open bolt design, the way I have read tho is that the frt for his designs are only for ########s use? But depending on what you do and how you make it they may let you have the design, nothing is for sure with the tech's, what may work for one guy may not work for another.
The process to get approval is well complicated, I am just starting out gathering peices, I have talked breifly with the tech department through emails and will give them a call this week to get started on my build.
One of the neater builds was in the shotgun news, I think some time a couple years ago and that one used the fire control group out of an ar15 as the trigger and hammer, they mod'd the bolt to be hammer fired using the ar15 firing pin and spring, they have to add a long tube to the back of the bolt so that it can never be full auto.
I am by no means even close to an expert on any of this, I am just plodding my way through it like others have, to hopefully get a sten design that they will let me register.
I can send you some more info that I have gathered, mostly just what forums are out there to see other builds, pm me if you want them.