Knickerbockers (4,5)
I believe the answer is:
plus fours
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">knickerbockers</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for plus fours that I've seen before include "leisure wear" , "Sportswear" , "Baggy sports trousers" , "golfer's wear" , "Bags" .)