The car used in the Public Broadcasting System series, The Prisoner, was a Lotus Seven S II. The prisoner claimed to have built it and could have because it was available as a kit in England. The license was KAR120C, and Caterham currently has the plate.
"A lasting memory and still an inspiration for man Seven owners was the> appearance of KAR120C in the TV series 'The Prisoner'. Two KARs appeared, the> 'real' one, normally the Lotus demonstrator, and a second lookalike seen here with the Prisoner himself, Patrick McGoohan, and Graham Nearn of Caterham Cars. McGoohan repaid Caterham's efforts in preparing a car for filming virtually overnight by posing for a series of photographs that were used in advertisements for some time after."
The KAS120C was the Lotus S2 demonstrator. This all happened in 1965; McGoohan himself contacted Lotus, asking for an Elan to use in the series. Graham Arnold, the marketing director for Lotus, arranged for McGoohan to see both the Elan and Seven; McGoohan chose the Seven. This was find with Arnold, since Mrs. Emma Peel was already driving an Elan...
KAR 120C had been delivered back to Lotus and sold when McGoohan came to ask for the car back again, on short notice, for another short shot. There was no car available at Cheshunt, but Caterham Cars were able to help out. The real KAR 120C had been Cosworth 1500 powered, but Caterham's team worked through the night to convert an older 105E Seven to look like KAR 120C. The substitue car was painted properly and had such details as stoneguards on the lights. It was> this car that appeared in the final episode of the series.
During the opening sequence of the show, the car was static against a moving backdrop. The end sequence was shot in one of the tunnels at Heathrow airport and purportedly showed McGoohan in the Seven roaring down to his Controller's headquarters.
Graham Nearn of Caterham Cars drove the car to the set for the final episode to be shot and found himself recruited as an extra. He can be seen dusting off the car and posting the keys through McGoohan's letter box, prior to the hero's arrival. The attached photos were taken after the filming was complete.
(Pictures and some descriptions are from Jeremy Coulter's Seven book.)
Thanks to Chris and Skip for this information.
When I have a hard time describing what the car looks like, I just refer to this program, and people almost always have an immediate recollection.