The HL310 has etched into the envelope both the maker Burndept and the words 'Super Valve'. The HL310 is is general purpose triode.
Burndept was a UK manufacturer who made a small selection of valves from 1925. In 1927 the company went into receivership to be reformed in 1928 as Burndept Wireless (1928). The new company made equipment not valves.
The lettering on the reverse looks like RAS or RAL with the letter B below.
Looking under the gettered part of the envelope one can see the vertical electrode assembly. The anode is a rounded ended box with the grid wire running parallel to the anode. The filament is broken.
The base has simple split pins with wire soldered at the top. The base moulding carries the words Burndept and Super Valve.
The wide glass tube envelope is 25 mm in diameter, and excluding the B4 base pins is 77 mm tall.
Reference: 1003, 1004 & 1043. Type HL310 was first introduced in 1925.