In reply to muppetfilter:
> Or is it part of the tory plot to destroy the BBC .....
No that explanation falls on Occam's razor, it was entirely self-inflicted - due to hubris, malice, the wish to harm their political opponents and a sense of invulnerability - after all, McAlpine could scarcely prove that he WASN'T a child-molester, could he?
There was no need to lure the BBC into smearing McAlpine on the basis of flimsy, unchecked, and largely discredited evidence, they were gagging to do it. The difficulty would have been to stop them, which would have required all their mouths to be tapped over. Does anyone seriously doubt that the broadcasting arm of the Guardian saw a golden opportunity to simultaneously escape from their own difficulties and also to assasinate a political foe, and found it irresistible? It was too good to be true! Unfortunately for them, what seems to be too good to be true, normally is. In this case, Lord McAlpine managed the normally impossible feat of proving a negative - he managed to prove that he was NOT a paedophile, even for most of the "no smoke without fire" merchants. This was what undid the BBC, also their hangers-on and fellow travellers like George Monbiot and Sally Bercow. That and their inability to resist triumphalist gloating, while burnishing their pretended concern for a genuine, but still delusional, victim, Steve Meesham.
They had the chance to kick an already shaky and embattled coalition while it was down, possibly even to bring the government down, and were wetting their nickers in excitement. They even had an element of plausible deniability, in that they did not actually directly name him - knowing perfectly well that the name would come out instantly and they laid all the signposts to ensure that it did. That this feeble piece of disingenous cowardice did not ultimately do them any good was not for want of trying - willing to wound, but afraid to strike, to strike in any way that they thought anyone could retaliate directly at them.
No need for any conspiracy theory of any greater complexity than this.