The UL44 is described by Mullard as a line timebase output pentode, what the Americans call a sweep tube. The 100 mA heater is for heater chain use, that is putting valves in series across the mains supply. A television is a complex device and normally required many valves and this is why the 300 mA chain became the standard. This valve was probably used for small black and white sets only.
It is clear that this valve was rescued from a set. The discolouration inside the glass shows the effects of electron bombardment.
The base is of the intermediate type of B8A base cap. Originally an all glass valve was fitted with a metal skirt with locating pip and spigot. Here the spigot has been omitted and in the final form the glass was moulded into the same diameter as the metal skirt and formed with a locating pip. The advent of B7G and B9A bases moved away from equi-spaced pins and obviated the need for a locating pip.
The thin glass tube envelope is 20 mm in diameter, and excluding the B8A base pins, is 71 mm tall.
References: Data-sheet & 1040. Type UL44 was first introduced in 1948.