The Monoscope tube
This is a Monoscope tube, based on a CRT gun assembly and the target with the pattern on it in the bulb. The connection on the side of the bulb is for the anode. The pip on the far side is the evacuation seal.

This tube, a "Monicon" was made by Cathodeon is a type C912 and the label says "Rediffusion London" which would be the wording or logo for the caption on the test card.
This particular tube is broken, the getter has gone white as the vacuum has failed and the air has got in RIP.

Cathodeon Monicon Brochure

RCA 2F21 monoscope tube data sheet 1946

RCA 2F21 monoscope tube data sheet 1954
Restoration article