Jill Dando cottoned onto savile & his paedo ring. Dando's investigations coincide with a time that the police were receiving regular letters from someone purporting to be close to savile & who said that when savile falls, "&, he will fall, he'll take well known personalities & past politicians with him." Perhaps Dando was getting these letters too, the pigs were covering them up.
So Dando got her dossier together, perhaps she got given one. She may have talked to people about it, her fiance, her friends etc She may have got drunk at her engagement party only a few weeks before she was killed. Cliff Richard was at her party, she & Richard were friends. Richard was questioned in the aftermath of her murder. Perhaps Cliff heard that Dando was onto savile, perhaps Dando told Cliff Richard what she was up to. Either way, savile found out. Savile was hooked up with the political hierarchy. He spoke to Blair &/or Campbell & voila, our own MI6 assets were used to assassinate Dando in broad daylight on her doorstep without the authorities getting anywhere near to busting the bastard! In fact, they botched the investigation & then got desperate, & inexpertly fitted up Barry George, a man it is no known is almost completely & utterly incapable of the act.
So, briefly

Dando tells Cliff she's onto savile without knowing he's in on it. Cliff tells savile, savile calls in favours from the top, Campbell calls in the wet worker. Guys a pro, doesn't get ID'd, pigs deliberately cock-up investigation or deliberately cover up the real killer by busting George.
Seems I'm not alone having caught onto this, because this youtube preview of a new documentary into Dandos murder appears to suggest a very similar string of events -
[video]www.youtube.com/watch?v=WLAXRn3vesI[/video]