The CV1099 is a triode hexode mixer valve (prototype X66), the CV denotes a specification for the UK government. Another close commercial valve is the 6K8G.
The triode was designed for local oscillator use and an injection voltage of 10 V peak to peak was produced. The hexode mixer took the signal into the top cap grid, thus maintaining the greatest separation between grid and anode circuits.
The electrically identical VR99 is in a classic envelope. It is probable that this exhibit is a post WWII valve made for replacement purposes.
The internal coating extends round all of the envelope.
Looking up from the base shows the coiled heater and the grid of the triode. Clearly the two sections are stacked vertically - not the construction of the 6K8G.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 94 mm tall.