This exhibit is marked on the glass as a glowswitch and Made in England. The voltage rating on the base is 230 - 250 Volts.
Inside are two vertical plates with a wire from one that approaches the other. The design looks to be that at a given voltage the small gap will break down causing ionisation of the gas filling and thus triggering a larger current flow between the main plates.
It is possible that this would have been used as a low power glow modulator.
The glowswitch is fitted with a small bayonet base.
The plates are in alignment.
Here the trigger electrodes can be seen above the main plates.
The thin glass tube envelope is 20 mm in diameter, and including the bayonet base is 76 mm tall.
Updated October 28, 2015.