The 1950s and into the 60s RAF hard hats were a two piece arrangement, with a soft (blue cloth) inner which contained the headset, (and looked not dissimilar to a WW2 Russian tankies' helmet), and an outer fibreglass(?) shell - which was just that, a shell with nothing else except a visor attached.
I'd be guessing that the photograph you saw might have been a crewman, probably a back seater, wearing only his 'inner'. I don't know whether there was much to be gained for the blokes down the back of V bomber wearing their hard hats most of the time, as they didn't have ejection seats, and if they were going to try (the operative word being 'try') to get out, they'd have lots of time to put the outer shell on over their cloth inners before 'egressing'.