There's a piece by Tom Mangold in the Evening Standard of 14 April, entitled 'Why Greg really fell out with Tony'. It's not available online but here is a substantial excerpt:
The inside story of relations between the Government and the BBC in the last year is only now beginning to struggle into the light. Here, I can reveal for the first time the scale of the personal breakdown in the relationship between the director-general, Greg Dyke, and his friend the Prime Minister, Tony Blair.(Hat tip: Anthony Cox.)Last July, even before David Kelly committed suicide, as Alastair Campbell continued to bombard the BBC with complaints about its war coverage and alleged anti-Government bias, Dyke snapped. In rage and frustration with his former friend Blair, he told other friends that he wanted to put a substantial part of his own private fortune into helping the formation of a new Labour Party that would end Blair's run as leader.
In a state of considerable anger, described by one witness as "a rant", Dyke, editorial chief of the most powerful and trusted news organisation in the world, gave vent to his fury.
He told friends he had had enough of Campbell's bullying of BBC news, that Blair was almost certainly behind these attacks, and that he was personally prepared actively to help engineer the removal of Blair by promoting a new political party to which he would donate three million pounds of his own private fortune.
.....
Dyke's unconscionable fury with his former friend seems to support the views of top broadcast executives such as Will Wyatt, former managing director of BBC TV, who was deeply opposed to Dyke's appointment as D-G in the first place. "I thought his politics disqualified him," Wyatt has written, adding that Dyke's gift of £50,000 to Labour and his open support for the party as a cheerleader was potentially dangerous for the editor-in-chief of the BBC, who was traditionally impartial and whose politics were best left unknown. The prospect of a strong-minded, emotional, impulsive and politically active D-G worried not only Wyatt but other people within the BBC news division.The ultimate irony is not that Dyke's love affair with Labour created any editorial bias towards Government in the BBC's news and current affairs divisions, but that his fury at what he regarded as Blair's personal and political betrayal of their friendship may have skewed his own judgment such as to have rendered him temporarily unsuited to handle, with the required cool detachment and strict political neutrality, the gathering crisis at the corporation.
By mid-July Kelly had committed suicide and Gilligangate broke out as a national scandal. I know for a fact that cool, professional minds at the top of the BBC news hierarchy created a strategy for dealing with the crisis, which was then impulsively hijacked by Dyke.
As a consequence, during the bitter battles between the BBC and Government throughout last year's long, hot summer months, there can be little doubt that, as supreme head of BBC news and current affairs, Dyke did help to set the tone of seemingly blameless arrogance and aggressive defensiveness that helped damage the BBC's case both in the eyes of the public and subsequently in those of Lord Hutton. "Greg said several daft things in private," says [Melvyn] Bragg, who remained very close to Dyke during the crisis...
...Another source, who was also told the same story, adds that Dyke deliberately rejected an olive branch from Number 10 at the height of the row.