I had a feeling that was the clue. I assume you agree it links with the wordplay in 24a.
The puzzle was published in April 2004, five months after Iain Duncan Smith, aka IDS, was deposed as leader of the Opposition. I took it as a reference to his political career being effectively finished. It was the Guardian, after all …
But if you mean it’s the last three letters of 10a you can’t find, I think they come from “Present not wrapped up” in 14a, that being HAND, verb for to present, without the final D, ie not wrapped up or finished.
Thanks to Kristi, Quisling and Jono for the information. I thought I'd give this a go, and found it quite tough.
I can't see the wordplay for 5d., though I think it comes from 1d.
I wonder about the significance of the four first letters. Perhaps they formed the setter's name?
Yes it was the HAN we couldn't match with "present" - we considered needing to lop off a letter for both ends, which came up with nothing (except a vague connection to "thank" but not really a match). We also considered lopping off only the last letter, and even thought of "hand" but dismissed it as not being a good match either! I can see it though.
Good luck with 13. There is quite a detailed discussion of it on an earlier thread, which I can point you to if you wish. We solved it, after a fashion, but there’s a loose end that requires tieing up. Maybe you will have better fortune!