There have been a lot of duff clues from this crossword recently! This one is just ungrammatical. 'I'd led' can only mean 'I had led' - the construction hinted at by the wordplay can only be 'I'd have led', which clearly doesn't equal the answer!
Cryptic crosswords are all about accuracy! If there wasn't an accepted code every clue would be insoluble. This is sloppy cluing, from basic incorrect grammar - as a compiler myself I (and every other compiler I respect) would reject it and rewrite it.
ok then. 'have' applies to the letters obtained from the rest of the subsidiary: the letters 'id' HAVE the letters 'led' (HAS would be ungrammatical in this case)