Our best guess is that this is a CT-10 general purpose triode. The image in 1003 is a tubular envelope and not the balloon we have here. But the Type clearly starts CT and ends in 0 making the CT-10 the most likely valve.
Looking under the silvering one can see the 'C' stamped into the bright anode. The single grid is held just within the anode space and the filament appears to be a single inverted 'V'.
The base bakelite is embossed with the Cleartron name, British Made and the CT logo in the centre.
The balloon envelope is 42 mm in diameter, and excluding the B4 base pins is 101 mm tall.
References: 1003 & 1043. Type CT-10 was first introduced in 1927. See also 1927 adverts.
Updated May 15, 2019.