Parker Duofolds had been made in the UK since the early 1930s, then generally following the contemporaneous American designs and often using American parts. These are rarely seen today.
The far better known UK Duofolds were introduced after WWII, starting with the Duofold NS, New Style. These had arrow clips and were button fillers, and were made in England and in Denmark for English distribution. The AF Duofold, initials to mean Aluminium Filler, appeared in 1948, and were very popular pens. Their aluminium mechanics were very sturdy and these were wonderful writers, with soft English nibs.
Finally, 1953 brought the final significant version, the New Duofold, aerometric fillers.