The issue was not Andrew Gilligan. Various newspapers had made the same allegations as the BBC, but Alistair Cambell and Blair are both aware that attacking the BBC guarantees the support of the Murdoch press.
It was essential for Campbell to keep the pressure on the BBC to ensure he had at least two national newspapers on his side.
David Kelly was just collateral damage.
Like Gareth I am Old Labour, but I am reaching the point where even 5 years of real Tories under Ian Duncan Smith seems preferable to the self-serving crypto-Tory party that Blair/Straw/Blunkett/Hoon are running.