I read about the BT Buckingham Palace installation in the BT Magazine in the 1980s. As well as some old phones being adapted because The Queen liked them, including one given to George VI her father, the Monarch(?) (aptly enough!) PABX had to be adapted to cope with a large number of manual extensions that dialled the operator on lifting the handset.
I'm a little surprised as the ventilation slots suggest a 746 but the cord suggests an 8746 or ... an illicitly converted 746?
Apparently when connecting the Queen Mother to The Queen the telephonist had to say "Your Majesty? Your Majesty, your Majesty".
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