Markings as follows

On barrel:

PARKER DUOFOLD
REG.T.M.
MADE IN ENGLAND

JOHN M. MOORWOOD LTD
"THE ROLL MAKERS"
STEPHENSON RD
SHEFFIELD

(see: http://www.davyroll.com/docs/history.htm)

Nib:

PARKER
DUOFOLD
14K
PEN
N

Cap:

REGD. NO. 784404

I think I might have answered my own question. Parker Duofold AF (Aluminium Filler). English. 1948-1953.

With an engraving........:-)

That should be an "Al-u-min-eum" filler.....

John