The BBC article claiming they have the tapes is around here somewhere... I read it here...
The tapes mentioned are apparently those of another BBC reporter, whose report on their flagship Newsnight programme made many of the same charges, but crucially, didn't directly accuse Downing St communications director Alistair Campbell of 'sexing up' the dossier as Gilligan did. So the BBC can presumably prove that Kelly said that the dossier was sexed-up, if not in those exact words, but not that he said Alistair Campbell was responsible for doing so. Campbell is more or less Blair's Karl Rove, so that's important at least in the context of UK politics.
Overview as of this morning, here:
http://www.cnn.com/2003/WORLD/europe/08/12/uk.hutton/index.html