pepperpot99 - you've badly misremembered what happened. Gilligan made two mistakes in a live radio interview (not a printed article), firstly strengthening Kelly's statement that the 45-minute claim in the report was 'unreliable' to a statement that the Government 'probably knew it was wrong'. And secondly, describing his (anonymous) source as an 'intelligence service source' when he should have said 'one of the senior officials in charge of drawing up the dossier'.
Obviously neither of those mistakes did anything to out Kelly. And neither of them detract from the main point of a very important story and a brave piece of journalism - that the 'dodgy dossier' had indeed been 'sexed up', which has now been admitted by everyone involved, including both Blair and Campbell.
David Kelly's identity became public because Kelly told his employer that he'd spoken to Gilligan, and they cynically decided to reveal his identity to the press to attempt to discredit the original story (by inserting clues in a press release and then responding to any wrong guesses that were put to them). This in turn led directly to Kelly's disgraceful public shaming by the Foreign Affairs Committee.
Obviously Gilligan wasn't entirely perfect, misspeaking in a live radio interview, but did break a story of major national interest, which has now been vindicated, and did nothing to compromise the identity of his source.