This valve is either a type Barion or is an LF & Det made by Barion. We cannot find details of Barion as a maker or reseller to confirm but a Type of LF & Det is most probable. But we do know from the envelope that the valve is British made and has a 2 Volt filament.
On test on a 2 Volt supply the filament current was 0.19 Amp and the dull glow suggests that the single inverted V filament is oxide coated.
The printed lettering and view of the box anode.
The construction uses top and bottom mica supports and the anode is ribbed for mechanical strength from the thin sheet nickel. The filament top support can be seen in front of the anode. Note that the filament support is welded to the wire that is sealed into the pinch. The construction method was to assemble the electrodes onto the main anode supports that were formed into the pinch. The other electrodes were then connected to the shaped wires from the pinch by spot welding. Later miniature valve construction required higher precision and the electrodes were assembled in specialist jigs and then the whole assembly would be spot welded to the pressed glass foot. See EF80 Assembly.
Note the spot welds holding the anode to its supports.
The balloon envelope is 48 mm in diameter, and excluding the B4 base pins is 82 mm tall.