The 10P13 is an output valve, designed for television service in both audio and frame timebase circuits. The 100 mA heater chains were used in post WWII monochrome receivers where few valves were needed. The 2.6 Watt output would have been more than adequate for domestic use.
This valve also appeared with an IO base as the 10P14
Inside the anode can be seen the bright beam plate.
The earliest form of the B8A base with locating pip on the metal skirt and central alignment spigot.
The envelope has the printed words Made in England and BVA.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 64 mm tall.
References: Data-sheet & 1040. Type 10P13 was first introduced in 1948.