Unknown tag lifted, holding lead on springer spaniel (3-3)
I believe the answer is:
yes-man
'spaniel' is the definition.
(thesaurus)
'unknown tag lifted holding lead on springer' is the wordplay.
'unknown' becomes 'y' (algebra).
'tag' becomes 'name' (I've seen this in another clue).
'lifted' says the letters should be written in reverse (going up in down clue).
'holding' is an insertion indicator.
'lead on' says to take the initial letters.
The first letter of 'springer' is 's'.
'name' written backwards gives 'eman'.
'eman' enclosing 's' is 'esman'.
'y'+'esman'='YES-MAN'
(Other definitions for yes-man that I've seen before include "Flunky" , "Sycophant" , "He never dissents" .)