Clare Balding , Stephen Fry, anyone who has the public's affection for a substantial period without seemingly making an effort, and avoids negative comment. David Starkey will never make it; no warmth. Derren Brown rules himself out for hinting that he might be one
to be fair, derren was just making a joke, he didnt say it seriously
dont know who half of those mentioned are ... id have thought to qualify you must be very well known ... i doubt there are many people who dont know who stephen fry or brucie are... but charlotte green? or dennis skinner?
and the sports people are unknown names! (i get why you mentioned them, but they are not 'national treasures' in the sense of stephen fry etc, they are 'treasures' in a different way)
dont agree with clare spalding really, but id agree on babs, julie walters and judi - though not so much maggie smith.
thenry i think is on the usa treasures... but bill clinton??