I've just had a go at sticking the photo in Photoshop and trying to bring up the poster on the wall (left side of the picture) But I can't make it readable. Maybe there is an expert in Photoshop who can do just that. I would say it is not WW2 because there are no paper strips on the glazing. No gas masks to be seen at all in the area either. Clothing styles look to be WW1 era I would think. ..Bingalau..
Woolwell. Didn't the RAF keep using Army uniform for a while after they were formed? If so this man could well be RAF. One of the other gents looks like he has a typical WW1 type moustache. The building itself doesn't look big enough to be a munitions factory. ..Bingalau..