Ground station MVZ

The attached picture has appeared on ARG with a request for the station ID info.
This call (MVZ) does not show in any of the list I have and in spite of extensive googling nothing has been found.
From the picture I think we may safely conclude the following……………

It is a UK air/ground/air station operating duplex (separate frequencies for A/G and G/A as shown in the callsign board.)
The mode is CW (Morse) not voice.
From the clothing – civilian station.
From the frequencies displayed, date is either before or soon after August 1948. That is the date when the ITU rehashed frequency band allocations . After that , for aeronautical use,the band in question stopped a 3950kcs.
Possibly useless info …the receivers in use are CR100s – the transmitter is remote.(CR100 came into use during WW2)

My best guess is something similar to Shanwick but much earlier.Probably over-water routes or uninhabited areas.
It isn’t Birdlip, Uxbridge or London.(MVB, MVU, MVX & MVA)

Any ideas very welcome.