Gordon Brown has exhibited “Stalinist ruthlessness” at the Treasury and has treated his Cabinet colleagues with “more or less complete contempt”, according to the Chancellor’s former top civil servant.

In an unprecedented attack, Lord Turnbull claimed that Mr Brown took an “insulting” approach to other ministers, expecting them to accept what he decided without discussion.

The eve-of-Budget character assassination by a man who was Mr Brown’s own permanent secretary at the Treasury for four years will send shock-waves around Westminster. It will revive questions about whether the Chancellor has the team-leading abilities to be Prime Minister.

His management style has been the subject of repeated private complaints from Treasury officials, who are some of the most unhappy in the Civil Service, with a very high turnover. There has also been criticism from some cabinet colleagues frustrated at his high-handedness. It is the first time, however, such a high ranking and respected official has openly attacked the Chancellor in public. After serving Mr Brown, Lord Turnbull went on to become head of the Civil Service as Cabinet Secretary from 2002 to 2005.

The former mandarin told the Financial Times that Mr Brown had a “very cynical view of mankind and his colleagues . . . He cannot allow them any serious discussion about priorities. His view is that it is just not worth it and ‘they will get what I decide’. And that is a very insulting process.”

He continued: “Do those ends justify the means? It has enhanced Treasury control, but at the expense of any government cohesion and any assessment of strategy. You can choose whether you are impressed or depressed by that but you cannot help admire the sheer Stalinist ruthlessness.”

Under Mr Brown, the Treasury has turned from a small department that controlled the nation’s finances, to a big-spending department that controls the detail of policy across the entire government.

The Chancellor has made many enemies in the parliamentary Labour party but very few dare speak out, calculating that it is impossible to stop him becoming Prime Minister.

Alan Milburn, the former Health Secretary, and Charles Clarke, the former Home Secretary, launched a website to promote new policies in what was widely seen as an attempt to get a serious candidate to stand against him.

David Miliband, the Environment Secretary, has repeatedly rejected calls for him to stand against the Chancellor, and so far the only declared candidates are the two left-wingers John McDonnell and Michael Meacher, both of whom have no chance of winning.

Lord Turnbull noted that the Chancellor tended to keep out of the limelight when difficult decisions had to be taken. Comparing him to T. S. Eliot’s “mystery cat”, who was never to be found at the scene of a crime, he said: “The Chancellor has a Macavity quality. He is not there when there is dirty work to be done.”

Although Lord Turnbull praised achievements such as independence for the Bank of England, he said Brown “belittles” ministers by turning to outsiders for advice rather than talking to the department responsible for the policy.

And he added: “The surprising thing about the Treasury is the more or less complete contempt with which other colleagues are held.”

Departments were told only at the last minute what their Budget settlement would be, said Lord Turnbull. “That has been impressive, but in a sense reprehensible. There has been an absolute ruthlessness with which Gordon has played the denial of information as an instrument of power.”

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