Father's fountain pen: information much appreciated

[Escaliba]

Whilst going through some of my deceased father's papers, I found a fountain pen which I believe must be a Parker and dating from the 1950s at the very latest, possibly earlier.
Have attached photos and would welcome any information about this pen.
Can anyone put a closer date on it?
Many thanks.

[jar]

Looks like one of the UK Duofolds, likely one of the "New Duofolds" with the aerometric fill.

[Marsilius]

Yes, a nice Parker, too. Maybe your this pen is hinting that you have the makings for starting a great Parker Duofold and Vacumatic collection? . . .