They were often worn "Indy-style" to the side too though. Since soldiers and civilians pretty much had to have their masks with them at all times, this would be the easiest way to carry them on a day-to-day basis. The way they're being worn above is the way they would be worn in combat conditions, or on the march. For parades, periods of leave, R&R and all other times when full kit wasn't being worn, they'd often be slung across the shoulder to the hip.
Pity the poor civillians though - nothing as cool as the Mark VII for them!

They only got draw-string bags or cardboard boxes with a length of twine for a shoulder strap! At least if you were an ARP warden or part of the emergency services, you might have had the military style respirator and case. (As in the first post - I think that badge is for the "Auxilliary Fire Service")
(By the way - Anyone familiar with the Britcom "Dad's Army", will have seen plenty of MkVIIs and VIs in action!)