By Nick Assinder
Political correspondent, BBC News website
Lord Turnbull said it himself when declining to be interviewed about his views on "Stalinist" Gordon Brown - "I think I've done enough damage already".
Mr Brown will not be smiling at Lord Turnbull interview
Few will argue with that. In what appeared to be an unprecedented intervention by a top Whitehall mandarin, Lord Turnbull gave weight to pretty much all the failings attributed to Mr Brown by his critics throughout his government career.
In an interview for the Financial Times he said the chancellor was ruthless, treated other ministers and civil servants with contempt, refused to listen to colleagues, imposed his own views, used denial of information as an instrument of power and was never around when trouble hit.
And, probably most crucially, Lord Turnbull said the effect was to deny the government cohesion or any assessment of strategy.
Only the claim, once attributed to 10 Downing Street, that Mr Brown suffered "psychological flaws" was missing from the catalogue.
The remarks, which Lord Turnbull claims were not for public use, would have been bad enough at any time from the man who served as Mr Brown's permanent secretary for four years before becoming Cabinet Secretary from 2002 to 2005.
But coming on the eve of Mr Brown's 11th, and very likely last Budget, and as he prepares to take over from Tony Blair within a few months, they could hardly be more damaging.
Mr Clarke has raised concerns over Mr Brown's style
They play into all the fears expressed by Mr Brown's critics, including former minister Charles Clarke, who last year raised his own series of concerns about Mr Brown's personality or way of working.
And they add grist to David Cameron's line that Labour MPs fear Mr Brown will make a disastrous prime minister but do not have the guts to challenge him. There is now likely to be much more of that during the Budget debate.
And one of the possible outcomes of this interview might be to intensify the search by the chancellor's critics for a heavyweight figure to challenge him for the leadership.
There is, however, another take on all this.
Firstly, some of the chancellor's supporters - like Labour chairman of the Treasury select committee, John McFall - point to the fact that some of the criticisms may actually be seen as strengths in the chancellor.
Mr Cameron is likely to refer to remarks in budget debate
For example, Lord Turnbull himself said, in relation to Mr Brown's behaviour: "You can choose whether you are impressed or depressed by that, but you cannot help admire the sheer Stalinist ruthlessness of it all."
And Constitutional Affairs Minister and would-be deputy leader, Harriet Harman, insisted her 25 years experience of working with Mr Brown showed he did listen.
She added that "if you want to make change for the better then you do have to have strong political leadership".
"All I can conclude is not all civil servants admire strong political leadership".
It has also been noted that, in evidence to a Commons committee in 2005, Lord Turnbull criticised former US ambassador Sir Christopher Meyer for attacking ministers in his autobiography.
He urged the committee to: "Ask Sir Christopher what thought he gave to .... the effect of patronising and derogatory comments in relation to elected politicians whom an ambassador has been paid, and paid handsomely, to serve".
And the prime minister's official spokesman said: "I think in the interests of good government it's a wise rule that says civil servants should not become the story."
And that will be the line pressed by Mr Brown's supporters.
It is that the criticisms really suggest the chancellor will make a strong, powerful and determined leader and that there is an element of bitterness in Lord Turnbull's remarks which reflect the irritation from top civil servants that they are no longer being allowed to run the show their way.
Still, with the leadership crown appearing now to be within the chancellor's reach, he could probably live without help of this sort.