This was the first televised episode of the series not based on any of the Leslie Charteris stories or novels. It was also the first color episode to be shown.
In "The Queen's Ransom", the Queen in question was played by Dawn Addams, who at the time of filming was in fact a Princess, having been married to Italian Prince Vittorio Massimo since 1954.
The aircraft (G-ASUW) is a 1949 DeHavilland DH-104 Dove 1A (s/n 04256) fixed wing, multi engine. (2 DeHavilland Gypsy Queen 70 Mk 3, 6 cylinder air cooled, 400 hp each).
The footage of the white Jaguar Mk1 going off the mountain road and crashing into the quarry would appear again two weeks later in The Baron episode 3 Something For A Rainy Day [13/10/66]; and again in The Champions Episode 28 The Final Countdown [13/4/69]; Randall & Hopkirk (Deceased) episode 22 It's Supposed To Be Thicker Than Water [13/2/70] and in spoof spy tv show The Preventers/Hippy Daze [16/12/96]
At the end of the story, the bad guys are using a white Jaguar with French number plates. This Jaguar was a 1959 3.4 liter SE, with the UK registration number UKV 668. It is clearly right hand drive. The white Jaguar that goes over the cliff was, in fact, an old, gray Jaguar that had been hand painted to look white. The cliff was at Betchworth in Surrey, near the railway station.