The WELGUN was developed during World War II at Special Operations Executive’s Station IX (i.e. Station 9 for those who cannot read Roman Numerals) at Welwyn, England. It was designed as a cheap and lightweight sub-machine gun.
The example shown here is in the collection of the Canadian War Museum. As is the case with all museum, only a portion of the collection can be displayed. The Welgun and the Welrod silenced handgun were in the CWM’s weapons storage vault when I visited in 2007.
Here is a link to a video by the Royal Armouries on YouTube showing the earlier Norm Gun and the Welgun.