Monitor Type 56

Has anybody got any information on an Air Ministry ‘Monitor Type 56’, please?

This is an oscilloscope unit and (very heavy!) separate power supply, which I assume was optimised for testing a particular system, probably radar.
Dating to the early ‘50’s, there’s a modification label dated 1953.
I’ve discovered that A.P.2563BD covers this unit, but that document doesn’t look to be in the Kew online index.
Many thanks,
Andy