BBC did indeed release it's list of "Top 100" based on 30,000 respondents. 

BBC's numerical "rankings" of the 100 apparently weren't disclosed until, after the "poll" was rather heavily flogged in a series of broadcasts, in which each of the "Top 10" were advocated by various celebrities/authorities/commentators, and during which time a vastly larger number of "voters" called in. 

I seem to remember the final number on order of 130,000. Whether or how this affected final rankings, is apparently unknown. Obviously these people were if nothing else, in some degree, TV fans.

The Wikipedia article seems to fully accept the validity of the BBC "poll" (which was not at all focused on Scott). Further, the article implies (to me) that the poll revealed a decline, over time, in Scott's popularity with the British Public. 

Seems like a reasonable thesis, but without comparable "polling" data from previous periods, this is not more than interesting speculation on the part of whatever author is cited.

For deep background, Wikipedia itself has a number of (non-featured) articles that are somewhat relevant with regard to the rather complex topic of polling, including sampling error margin of error,  tracking poll, straw poll, and various other topics. 
I'm certainly uninformed.