At present I have no documentation for this clock, and it has no markings other than the labels for the controls and external connections, such as "LPS OFF", meaning lamps off, "RESET", meaning set the time, etc. Internally it is evidently hand built, with a few of the parts being obviously hand made but most being telephone exchange components. The lamp array is cut from ebonite and the offcuts used as brackets.  The standard of construction is extremely high, as good as that seen in high quality test equipment and high end consumer electronics of the period, which I reckon to be mid 1940s, perhaps a little later.

There's a door on the left side.	Behind is a control panel	Controls for setting the alarm time, and some other functions.
The front with cabinet removed.	With the fascias removed.  The rear of the top fascia is shown here.	Push to release latch allowing clock to hinge upwards.  Calendar is attached to base.
With the top (electrical) section lifted slightly many of the components can now be seen.	Fully lifted and the mains transformer and metal rectifier are clearly visible.	Viewed from above.  The synchronous motor is in the top left of this picture.
A close-up of the motor, cam and switch.	The calendar part is entirely mechanical.	The three uniselectors are different.
The control panel.	Calendar close up.	Do the capacitor markings suggest a date?

 

The clock mechanism

The clock relies almost entirely on electro mechanical switches.  The time source is a drop in "module" comprising a 240V 50cps synchronous electric motor with gearbox giving one RPM.  Attached to this is a cam which activates a switch that looks to have been taken from a relay similar to those used elsewhere in the clock.  This gives one pulse per minute.

The rest of the mechanism is built from relays and uniselectors and counts minutes, tens of minutes and hours.  These are displayed in two rows of lamps, the top row being hours (1 to 12) the first five lamps of the second row being tens of minutes and the remaining ten lamps being minutes (0 to 9).  

Further sophistication (complication) is found in the alarm and reset operations.

The calendar mechanism

This is entirely mechanical.  Every 12 hours a lever is pressed and this advances the day dial, e.g. A.M. Mon advances to P.M. Mon.  There's also a date dial and a month dial.  The month dial has a cam to set the number of days in the month.  February has 28 days on the cam, but every 4 years this is advanced to 29 by an extra lever pushed into place by an extra wheel that advances every 6 months and completes one revolution every 4 years.  A nice touch!

Uniselectors are also known as stepping switches and stepping relays.  In telephone exchanges this type of switch is used in a 2D arrangement known as a Strowger switch.

Mechatronics, see Mechatronics - Wikipedia. Maybe I should call this artefact a "Mechatronic Clock".

• Stepping switch - Wikipedia
• Telephone switches - Mark Csele
• Post Office Equipment for Radar - describes a special computer using uniselectors (4 Jan 1946).
  
• BBC Aldenham - interesting mention of scarcity of relays and uniselectors here
  
• The Electronic Cricket Scoreboard - built from surplus GPO uniselectors and relays in 1969.
• GEC Control Telephone systems
  

Other components

• The 3000 type relay

• Uniselector chronogram
• Modified  Beckman/Berkeley counter/timer
• Electric Clock World

• Westinghouse 1934
• Penwood Numechron 1930
• Synchronome 1931
• Synclock 1931

Early computers

• Zuse - nice labelling of relays
  
• The life and work of Konrad Zuse
• Bletchley Park
• The Manchester Small Scale Experimental Machine