This is a genuine GPO phone . I have some personal history with the origins of this phone and how I came upon it. Too nice to throw away. I stowed it away for last twenty years.
You can plug it into a modern socket and dial out and make calls, you can hear and be heard, but ringing circuit not currently working.
This is probably late 50's early 60's.
Check out the pictures at:https://trashnothing.com/pics/144825