LONDON, Jan 21 (Reuters) - A poll on support for Scottish independence found voters are split on the idea, with backing for Yes and No at 46% while 8% remain undecided, Savanta ComRes said on Friday. The poll put support for independence up 1 point to 46% and support for remaining in the union down 2 points, as backing for British Prime Minister Boris Johnson in Scotland fell further, dropping 16 points since October. The poll put Johnson"s net favourability rating at -62.