Patrick McGoohan was so taken by Portmeirion he used it as the location for his Village in "The Prisoner".
Future James Bond cast members in this episode: Lois Maxwell who would play Miss Moneypenny in 14 films starting with Dr. No, Donald Pleasence who would play Blofeld in You Only Live Twice and Martin Benson who would play Solo in Goldfinger.
The letters on the eyechart in the background of the doctor's office are backwards as if seen in a mirror.
This was the first of two Danger Man episodes filmed in colour. The next episode - the final one - would also be in colour. These two episodes were eventually combined with some additional linking shots and released commercially as "Koroshi". There were no closing "Koroshi" credits and no "Shinda Shima" opening titles; the two simply ran into each other except for the few minutes of linking footage. No reference in the film is made to Danger Man, although the ending credits have the signature series theme. There are minor differences between the episodes and the movie, with two being the most notable. In the series Tanaka (the chauffeur) is shown at the end in the airport with Drake, asking if he can get him anything; in the movie, Tanaka attacks Drake after Sanders' plane crashes and is knocked out by Drake (who finds a cult medallion on him). The other is more subtle: when Drake visits Rosemary in the episode she holds down the phone switch when using the phone, making it clear she is only pretending to help Drake; in the movie the shot is removed, making her actions more ambiguous.
Nit pick - OK the episode was not shot on location, but all the main baddies are Western. In the record store, Drake should have spotted his non-Japanese tail a mile off.