This valve is described as an Augetron electronic (electron) multiplier valve.
We believe that this could have been made by Cossor in the late 1930s.
By way of additional information: base caps of the style shown on the left of the photo were commonly used by M-OV and sometimes by Cossor during this period but that on the right-hand end is reminiscent of the style used on some Hivac valves of this time.
The secondary-emission photomultiplier principle was news during the 1930s and many industrial laboratories attempted to devise amplifiers using it, particularly for photo-cell amplification but also as a possible solution to the need for very high gain-bandwidth product required for television and RADAR. Most of the early types were not very successful but a few single-stage secondary emission valves did reach limited production in the late 1930s.
Visually it can be seen to have a stack of discs alternately metal and a ceramic former. Photomultipliers operate in the same way to give very high amplifications.
The wide glass tube envelope is 57 mm in diameter and, excluding the base pins is 216 mm tall.
Updated February 04, 2021.