This looks like an ordinary M-OV Type V24 dating from 1923 or 1924 and sold into the domestic market. The 'Type approved by PMG' BBC stamp was obsolete by August 1924. The type number (V24) should be etched into the glass but we did not observe this during photography.
The Marconi V24 valve was a development of the 'R' type aimed at improving the high frequency performance. The V24 was designed around 1917 and was used as an RF amplifier with a filament current of 0.7 Amps. The anode voltage would have been in the range 24 to 50 Volts. The V24 itself being an indication of the use of standard 24 Volt supplies of the type used on board ship for lighting.
The grid and anode connections are to side pips on the envelope and the single strand tungsten filament runs from cap to cap, with a spring for tensioning. The construction is co-axial with the helical wire grid surrounding the filament and fitting within the cylindrical anode. In this valve the 'U' shaped glass support holds two stout wire rods that attach to the anode and grid respectively. These electrodes are thus only supported at one end.
The thin glass tube envelope is 18 mm in diameter and, tip to tip is 71 mm tall. Across the side pips measures 28 mm.
References: 1003. Type V24 was first introduced¶ in 1919.